Fundamental Diet Principles & Why They Matter More As You Train Harder

Aligning Nutrition With Training Intensity, Part 1.

When training becomes more demanding, nutrition often needs reconsidering. Total energy intake may need to increase, carbohydrate requirements can rise considerably with longer or more frequent sessions, and the timing of food and fluids may become more important when recovery periods are short. Protein remains essential, although requirements don't necessarily increase in proportion to every change in workload.

These principles are reasonably well established in sports nutrition. Applying them to an individual training programme is rather less straightforward.

There comes a point in training when progress becomes harder to explain. You're following a programme, adding weight or repetitions where you can, and allowing what seems like enough time to recover. Yet performance begins to level off, fatigue becomes more noticeable, or sessions that once felt manageable start requiring more effort than they used to.

There may be several explanations. Training volume could have increased too quickly, sleep might be inadequate, or accumulated fatigue may be masking improvements that haven't yet become apparent. Nutrition deserves a place in that assessment too, particularly when training demands have increased without much consideration of whether food intake has changed alongside them.

I've always found it interesting how precisely people can approach their training while treating nutrition as something relatively fixed. They'll measure sets, repetitions, rest periods and progression, but eat much the same way whether they're training three times a week or six. They may have established a protein target, settled into a familiar routine of meals and developed a supplement regimen they're comfortable with. None of this is necessarily wrong. The difficulty comes when the workload changes and the diet remains much as it was.

The principles of good nutrition don't suddenly change because someone starts training harder. Adequate energy, protein, carbohydrates, dietary fats, vitamins, minerals and fluids remain important. What changes is how much may be required, which nutrients become more significant under particular conditions, and how little room there may be for persistent mistakes.

This is the first of two articles examining how nutrition should be considered alongside training demands. Here, I'll look at the underlying principles, what the research supports and where commonly repeated advice is less certain than it sometimes appears. Part 2 will deal with the practical application, including meal planning, carbohydrate intake and recovery strategies around different training schedules.

Understanding the demands of training

Before getting into individual nutrients, it's worth clarifying what we mean by training intensity.

In exercise science, intensity can refer to specific measurements, such as the percentage of a maximum lift, running speed relative to an individual's capacity or power output during cycling. Outside those settings, it's often used more loosely to describe how demanding a session feels.

For nutritional purposes, intensity alone doesn't tell us enough. Duration, total workload, frequency, the type of exercise and the recovery time available all influence requirements.

Consider someone performing three relatively short strength sessions each week. They may be lifting heavy weights, working close to their limits and making meaningful progress. Compare that with someone performing several hours of endurance training, regular conditioning and perhaps a couple of strength sessions as well. Both could reasonably describe their training as hard, but the total energy expenditure and reliance on carbohydrate can be quite different.

The same applies within individual sports. A powerlifter working with heavy loads and long rest periods isn't facing precisely the same nutritional demands as a bodybuilder performing high-volume sessions with shorter recovery periods. A recreational runner completing two short runs each week has a different fuelling problem from someone preparing for a marathon.

It's tempting to draw a simple relationship between training intensity and food intake, but nutritional requirements don't increase neatly in proportion to how difficult exercise feels. A short, demanding session may use less energy than a prolonged session performed at a lower intensity. Resistance training also places different demands on muscle glycogen from continuous endurance exercise, and those differences influence how useful particular nutritional strategies are likely to be.

Individual responses complicate matters further. Body size, training history, habitual diet, energy availability and digestive tolerance can all influence what someone requires and how they respond.

This is explored more broadly in our article on personalising supplements and nutrition, although personalisation shouldn't be confused with the need to make everything unnecessarily complicated.

I would begin by examining the training programme itself: how many hours are being completed, the type of work involved, how much has changed recently and whether the person is recovering well enough to repeat the intended workload.

Without that information, even apparently precise nutritional recommendations can be of limited use.

Energy availability and the cost of under-fuelling

Energy balance is familiar territory. Over time, changes in body weight are influenced by the relationship between energy intake and expenditure, although the processes involved are more dynamic than a simple daily calculation might suggest.

For athletes and people undertaking demanding training, there's another consideration: energy availability.

Energy availability describes the dietary energy remaining for normal physiological functions after the energy cost of exercise has been accounted for, relative to fat-free mass. Someone can be eating what appears to be a reasonable amount of food and still have insufficient energy available for the demands they're placing on their body.

This can become particularly relevant when training volume increases, calorie intake is restricted, or an athlete attempts to reduce body weight while maintaining performance.

The International Olympic Committee's 2023 consensus statement on Relative Energy Deficiency in Sport (REDs) describes the potential physiological and psychological consequences of problematic low energy availability. These may involve reproductive health, bone health, immune function, metabolism and sporting performance, although the effects vary considerably between individuals.

The evidence is substantial enough to take seriously, but the subject needs care. Not every athlete who feels tired is under-fuelled, and reduced performance isn't sufficient evidence of low energy availability. Training overload, illness, stress, inadequate sleep and other medical factors can produce similar experiences. Nor is there a single energy-availability threshold that reliably predicts problems for everyone.

Researchers have also identified differences in how low energy availability presents across populations. Findings from one group of athletes, or from a short-term experimental intervention, can't necessarily be extrapolated to everyone undertaking demanding exercise.

Nevertheless, prolonged or severe mismatches between energy intake and exercise demands can have consequences that extend beyond feeling tired during a session.

This is particularly relevant when someone increases training while attempting to maintain an aggressive calorie deficit. The aim may be to lose fat while preserving muscle and performance, but the nutritional and physiological demands don't necessarily accommodate that ambition.

I would be cautious about assuming that increasing exercise and reducing food intake are independent strategies that can simply be combined. The interaction between them deserves more thought, especially during weight-class preparation, demanding endurance blocks or prolonged periods of dieting.

We've discussed some of the practical challenges associated with restricted intake in our article on refuelling after a weight cut, although short-term competition preparation raises additional concerns and shouldn't be treated as a model for ordinary weight management.

Someone who notices persistent fatigue, unintended weight loss, recurrent injuries, menstrual disruption or unexplained reductions in performance should seek appropriate professional assessment rather than trying to diagnose the problem through diet changes alone.

For most recreational trainees, however, the initial question is less complicated: has food intake kept pace with the increase in training, and is there any evidence that recovery is becoming more difficult?

Protein: meeting requirements without losing sight of the diet

Protein receives considerable attention in sports nutrition, particularly among people who lift weights. Much of that attention is justified. Resistance exercise stimulates muscle protein synthesis, and dietary protein supplies the amino acids needed to support the maintenance and development of skeletal muscle.

The difficulty is that protein sometimes becomes the measure by which the quality of an entire diet is judged.

The International Society of Sports Nutrition's position stand identifies approximately 1.4–2.0 grams of protein per kilogram of body weight per day as generally sufficient for most exercising individuals seeking to build or maintain muscle. Some circumstances, particularly energy restriction, may justify higher intakes, although requirements depend on the person and the training programme.

For an 80-kilogram individual, that general range corresponds to approximately 112–160 grams daily.

These figures provide a reasonable reference, but there's little benefit in treating the upper end as a compulsory target for everyone. Once intake is sufficient, consuming more protein doesn't necessarily produce further improvements in muscle growth or performance. It may simply displace carbohydrate, dietary fat or other foods that would make the diet more appropriate overall.

A person regularly consuming 180 grams of protein but struggling to eat enough carbohydrate for prolonged training hasn't necessarily created a better nutritional strategy than someone consuming a more moderate amount of protein alongside adequate total energy.

Choosing protein sources

Protein quality deserves consideration, although the differences between foods and supplements need to be interpreted in the context of the whole diet.

Whey is well researched and provides a concentrated source of essential amino acids, including leucine. It's also convenient, particularly for people who struggle to organise meals around work, training or travel. Eggs, dairy foods, meat, fish, soya and appropriately planned combinations of plant proteins can also make valuable contributions.

For many people, the decision to use a protein powder is primarily practical. Someone who struggles to eat a substantial meal after training may find a shake easier to manage. Someone whose ordinary diet already supplies sufficient protein may have little need for one.

There are differences between whey concentrate and isolate, but I wouldn't describe either as universally superior. Isolate usually contains a higher proportion of protein by weight and less lactose. Concentrate may be more economical and can be perfectly appropriate for people who tolerate dairy well. The actual formulation, protein content, individual tolerance and price are more meaningful than general claims about one format being inherently better.

The discussion around protein powders is also a good example of why supplement format needs to suit the ingredient and intended use. Our guide to stacking supplements and choosing between powders, capsules and liquids covers some of the practical distinctions.

Ingredient quality matters as well. I've written elsewhere about why trustworthy supplement suppliers can be difficult to identify, particularly when two products appear similar on the label but differ in specification, testing or manufacturing standards.

Digestive tolerance

Protein also has to be practical to consume consistently.

Someone who experiences bloating, discomfort or gastrointestinal symptoms after a particular protein product may struggle to use it regularly, regardless of its nutritional composition. Lactose content, serving size, sweeteners, other ingredients and individual digestive conditions can all influence tolerance.

That doesn't automatically mean the person has poor protein absorption or requires digestive-enzyme supplements. Most healthy people can digest ordinary dietary protein without additional enzymes, and evidence supporting routine enzyme supplementation for otherwise healthy athletes is limited.

If digestive symptoms persist, identifying the cause is more useful than assuming a supplement will correct it.

I'd establish adequate daily protein first, choose sources that suit the individual and consider timing or delivery format where there's a practical reason.

Carbohydrates and the demands of repeated exercise

Carbohydrates are often discussed in relation to body weight, blood glucose or dietary preference, but for someone undertaking demanding training, their role in exercise metabolism deserves more attention.

During moderate- to high-intensity exercise, carbohydrate can make a substantial contribution to energy production. Muscle glycogen, the stored form of carbohydrate, becomes particularly important during prolonged activity and repeated bouts of demanding exercise.

The amount required varies considerably according to the work being performed.

A brief strength session with long recovery periods between sets doesn't impose the same glycogen demands as a prolonged run, repeated sprint training or a demanding conditioning session. Even two people completing similar workouts may differ in how much carbohydrate they need because of differences in body size, training status and the rest of their weekly activity.

Research by Burke and colleagues on carbohydrate availability for training and competition supports adjusting intake according to exercise demands rather than prescribing the same amount for everyone.

General sports-nutrition guidance commonly describes ranges such as:

Training demand	Approximate daily carbohydrate intake
Light training	3–5 g per kg body weight
Moderate training, around one hour daily	5–7 g/kg
Higher-volume endurance training	6–10 g/kg
Very prolonged endurance demands	Potentially more, according to individual requirements

These are illustrative ranges, mainly developed around the demands of sports training. They're not universal targets, and it would be misleading to tell every recreational lifter to consume 5–7 g/kg simply because they train regularly.

For someone weighing 80 kilograms, 5 g/kg represents 400 grams of carbohydrate per day. That's a substantial intake and may be appropriate for certain demanding programmes, but it shouldn't be recommended without considering the actual workload.

The more useful question is whether carbohydrate availability is sufficient for the training being undertaken.

Recognising inadequate fuelling

When carbohydrate availability becomes limiting, an athlete may struggle to maintain performance during prolonged or repeated high-intensity activity. Fatigue can develop earlier, perceived effort may increase and the intended training workload may become harder to sustain.

These symptoms aren't specific to carbohydrate intake, however. Poor sleep, inadequate total energy, accumulated training fatigue and illness can have similar effects.

It's also important not to overstate the relationship between carbohydrate and muscle preservation. Carbohydrate intake influences insulin and glycogen metabolism, and insulin participates in the regulation of protein turnover. That doesn't establish that eating more carbohydrate will automatically prevent muscle loss or improve recovery in every situation.

Adequate protein and sufficient overall energy remain central to the picture.

For someone undertaking demanding sessions, it may be useful to review the amount and timing of carbohydrate before assuming their training programme needs another change.

Rice, potatoes, oats, bread, pasta, fruit and other carbohydrate-containing foods can all contribute. During or immediately before exercise, digestibility may become more relevant than fibre content or the nutritional reputation of a particular food.

A large, high-fibre meal might be a sensible choice at another time of day but less appealing shortly before intense training.

Dietary fats and avoiding unnecessary restriction

Dietary fat provides energy, essential fatty acids and a means of absorbing fat-soluble vitamins. Fat-containing foods can also contribute protein, minerals and other nutrients, depending on what is being eaten.

Yet fats sometimes become the first casualty when someone tries to combine a high protein target with a fixed calorie allowance and enough carbohydrate to support training.

There isn't one dietary-fat intake that suits every athlete. Requirements depend on total energy needs, dietary preferences, food choices and the overall nutritional pattern.

As a general principle, prolonged and unnecessarily severe fat restriction is difficult to justify, particularly if it compromises essential fatty acid intake or overall dietary adequacy.

I would also be careful about claims linking particular fat intakes directly to testosterone or other hormonal outcomes. Some research has examined the relationship between dietary composition and hormone concentrations, but results depend on the populations studied, the dietary interventions and the surrounding circumstances.

Evidence that extreme restriction can affect normal physiological function shouldn't be taken to mean that increasing fat intake will reliably improve hormonal status in someone who is already adequately nourished.

Olive oil, nuts, seeds, oily fish, eggs, dairy foods and other suitable fat sources can contribute to a balanced intake. The proportions will depend on the rest of the diet and what the person is trying to achieve.

Nutrient timing and when it becomes more important

Nutrient timing has produced plenty of complicated advice over the years, much of it based on the idea that small differences in when someone eats can substantially change the results of training.

There are situations where timing genuinely matters, but they aren't the same for everyone.

For a person training three or four times weekly, consuming adequate energy and protein throughout the day is likely to be more important than meeting a narrowly defined post-workout window.

The situation changes when sessions are prolonged, carbohydrate availability is limited or the time between training sessions is short.

Someone completing a demanding morning session followed by another in the afternoon has less time to replenish glycogen than someone training again two days later. In that situation, what they eat between sessions can become a significant part of their preparation.

Before training

A meal containing carbohydrate and a moderate amount of protein may be useful before demanding exercise. The amount and timing depend on the individual, the size of the meal and how comfortably it can be digested.

Some people tolerate a substantial meal two or three hours beforehand. Others prefer something smaller closer to the session. There's no reason to insist on an identical routine for everyone.

High-fat or particularly high-fibre meals may be less comfortable immediately before intense exercise, although individual tolerance varies.

Training without eating beforehand

Fasted training isn't inherently problematic. Someone performing light exercise, walking or a short session may feel perfectly comfortable without breakfast.

For prolonged or demanding training, however, carbohydrate availability can become more relevant. The decision to train fasted should be considered alongside the expected workload, the person's previous food intake and their response to the session.

It's possible to perform demanding exercise while fasted, but that doesn't necessarily make it the best approach for performance or recovery.

During exercise

Carbohydrate intake during exercise becomes increasingly useful as duration and demand rise, particularly in endurance activities.

For shorter sessions, ordinary meals before and after training may be entirely adequate. For prolonged exercise, readily digestible carbohydrate can help maintain availability and support the intended workload.

The amount required depends on duration, intensity and individual tolerance. A short resistance session shouldn't be treated as nutritionally equivalent to several hours of endurance training.

After exercise

Protein intake after exercise can contribute to muscle protein synthesis, but the familiar suggestion that a shake must be consumed almost immediately after the final repetition is an exaggeration.

The evidence is more consistent with ensuring sufficient total daily protein and distributing intake reasonably across the day.

Carbohydrate timing becomes more important when rapid glycogen restoration is needed, particularly when another demanding session is scheduled soon afterwards.

Someone training once daily with adequate meals may not need to think about this in much detail. Someone training twice daily probably should.

The same emphasis on purpose and circumstances applies to getting the most from supplements. Timing can be relevant, but it should follow from a clearly identified need rather than becoming an exercise in scheduling for its own sake.

Hydration and electrolyte balance

Fluid requirements vary considerably between individuals and activities.

Exercise duration, intensity, temperature, humidity, clothing and body size all influence sweating. Even people performing the same workout in similar conditions may lose very different amounts of fluid and sodium.

The American College of Sports Medicine's position stand on exercise and fluid replacement discusses individualising fluid strategies and avoiding excessive dehydration. It also recognises the usefulness of electrolyte-containing fluids under appropriate circumstances.

For normal daily activity and shorter sessions, water and ordinary meals are generally sufficient. There is little reason to assume every gym session requires a specialised hydration formula.

Longer sessions, substantial sweating, hot conditions and closely spaced training sessions can make fluid and electrolyte replacement more relevant.

Sodium and chloride are generally the principal electrolytes lost in sweat, although potassium, magnesium and calcium are also present in smaller amounts. The concentrations vary between individuals, and fluid loss alone doesn't tell us exactly how much sodium someone has lost.

I've explored these differences in more detail in our article on what electrolytes are lost through sweat, alongside the wider subject of hydration for training performance.

There are practical ways to get a rough indication of fluid losses. Measuring body weight before and after a session, while accounting for fluid consumed and any urine passed, can help estimate sweat loss. It's an approximation rather than a precise measurement, since several factors contribute to changes in body weight during exercise.

It's also possible to drink too much.

During prolonged endurance exercise, excessive fluid consumption can contribute to exercise-associated hyponatraemia, a potentially serious reduction in blood sodium concentration. Advice to drink as much water as possible is therefore inappropriate.

Hydration should reflect the demands of the activity, individual losses and the circumstances in which exercise takes place. For some sessions, water will be enough. Others may require a more structured approach.

Micronutrients and nutritional adequacy

Training places demands on numerous physiological processes involving vitamins and minerals, but it would be misleading to suggest that exercise automatically creates a need for high-dose micronutrient supplements.

A more relevant concern is whether the diet supplies adequate nutrients while supporting the person's energy requirements.

Restrictive diets, limited food variety and sustained calorie deficits can make this more difficult. Certain athletes may also have particular risk factors associated with their sport, physiological characteristics or eating patterns.

Iron is one example. It's required for normal oxygen transport, and inadequate iron status can affect health and exercise capacity. Some endurance athletes and menstruating individuals may be at greater risk of low iron stores, but fatigue isn't enough to diagnose a deficiency. Supplementation should be guided by appropriate assessment.

Magnesium contributes to normal muscle and nervous system function, while zinc participates in numerous physiological processes, including normal immune function and protein synthesis. These nutrients are essential, but taking more than the body requires doesn't necessarily improve performance.

Vitamin D is also relevant in the UK, particularly during autumn and winter when sunlight exposure is limited. NHS guidance advises adults to consider a daily supplement containing 10 micrograms of vitamin D during these months, with year-round advice applying to certain groups.

That is established public-health guidance. It's not evidence that high-dose vitamin D supplementation will improve athletic performance in people who already have adequate vitamin D status.

Supplement format is another consideration, although claims that liquid vitamins are inherently better absorbed than tablets go beyond what can be concluded for every nutrient and formulation.

A varied diet remains the appropriate starting point for most people. Vegetables, fruit, pulses, whole grains, eggs, fish, meat, dairy or suitable alternatives, nuts, seeds and other foods can all contribute.

Food preparation and timing may need some thought when training becomes particularly demanding. High-fibre meals are valuable within a balanced diet, but someone with a sensitive digestive system may prefer lower-fibre options immediately before exercise.

There's no need to confuse eating appropriately for a particular session with avoiding otherwise nutritious foods altogether.

The place of supplements

Working in the supplement industry makes me particularly conscious of the difference between a product having an interesting formulation and someone genuinely needing it.

A well-formulated supplement may be useful when it addresses a specific dietary requirement or practical problem. Protein powder can make adequate protein intake easier. Carbohydrate powders can provide convenient fuel during prolonged activity. Certain vitamin and mineral supplements may be appropriate where dietary intake is inadequate or recognised public-health guidance applies.

What I'm less convinced by is the tendency to build complicated routines before establishing whether the ordinary diet is suitable.

There's also a difference between evidence for a nutrient, evidence for a particular ingredient preparation and evidence for a finished product. Studies using one formulation at a particular dose cannot automatically substantiate claims about another product simply because the ingredient names are similar.

This is one reason I've always considered sourcing, specifications and testing important. A product should be assessed according to what it actually contains, how it's manufactured and whether the evidence is relevant to its intended use.

The decision to combine supplements deserves similar care. Our article on stacking supplements and avoiding unnecessary overlap examines this in more detail.

Sometimes the more useful decision is to simplify an existing routine rather than add to it.

Applying the principles to different training schedules

It's easier to understand how these recommendations work by considering a few realistic training situations. They don't provide individual nutritional prescriptions, but they show what I'd examine before deciding whether someone's diet needs to change.

Three weekly resistance-training sessions

Consider someone weighing 80 kilograms who performs three resistance-training sessions per week, each lasting approximately an hour. Their goal is to increase strength and muscle mass, they're sleeping reasonably well and they have adequate recovery time between sessions.

I'd begin by looking at overall energy intake, whether body weight is changing in a way that suits their goal, and whether protein consumption is reasonably consistent.

Using the ISSN's general guidance, a protein intake somewhere in the region of 112–160 grams per day may be appropriate, although the final amount would depend on the individual. Carbohydrate intake also needs to be sufficient, but there is no reason to prescribe an endurance athlete's carbohydrate target simply because the person trains hard.

If their existing diet meets these requirements, performance is improving and recovery is satisfactory, there may be very little to gain from introducing complicated nutrient timing or an extensive supplement routine.

Strength training combined with conditioning and endurance work

Now imagine the same person adds two conditioning sessions and a longer weekend run while retaining their resistance training.

The increase in weekly energy expenditure may be substantial, depending on the length and intensity of the new sessions. Carbohydrate use will also change, particularly if those sessions involve prolonged exercise or repeated high-intensity efforts.

In this situation, I'd look at what they're eating on the more demanding days, whether they're beginning sessions with adequate energy available and how much time they have to recover before training again.

Their protein requirements won't necessarily increase dramatically if their original intake was already sufficient. Simply adding another protein shake may do little to address the actual nutritional change.

Increasing portions of carbohydrate-containing foods, adjusting meals around the longer sessions or using a convenient carbohydrate source during prolonged exercise might be more appropriate. The need for additional fluid or electrolytes would depend on the duration, environment and individual sweat losses.

I'd also look at the overall weekly pattern. Someone may eat adequately on the day of a particularly hard session but still struggle to recover if their usual intake remains too low for the work they're completing.

Training while trying to lose body weight

A third situation involves someone attempting to reduce body fat while maintaining a substantial training schedule.

Energy restriction may be appropriate for their goal, but the size of the deficit, the duration of dieting and the training load need to be considered together.

I'd be particularly cautious where an athlete combines a substantial calorie deficit with additional endurance work, frequent high-intensity sessions or inadequate recovery time.

Protein intake may need closer attention to support the maintenance of lean tissue, but it won't eliminate every consequence of insufficient energy availability.

Depending on the sport and the individual, it may be more sensible to moderate the rate of weight loss, reduce unnecessary training volume or place more carbohydrate around demanding sessions than to pursue the largest possible energy deficit.

Where weight cutting, persistent fatigue, menstrual disruption, disordered eating or other health concerns are involved, suitably qualified professional guidance becomes especially important.

Comparing the nutritional priorities

Training situation	Main considerations
Three weekly resistance sessions	Adequate total energy, consistent protein, sufficient carbohydrate and recovery
Resistance training plus regular conditioning	Increased energy expenditure, carbohydrate availability and meal timing
Long or closely spaced sessions	Rapid recovery, carbohydrate availability, fluids and individual sweat losses
High training load during weight loss	Energy availability, appropriate rate of weight loss, protein and recovery

There isn't a precise formula that can turn these examples into individual requirements without further information. Body composition, habitual intake, actual workload, training history and physiological response all influence what is appropriate.

What the comparison illustrates is that two people with similar body weights can have substantially different nutritional priorities, even if both describe themselves as training hard.

Where I would start

If I were reviewing someone's nutrition in relation to their training, I'd begin with the programme itself.

How often are they training? How long are the sessions? Has the workload changed recently? Are they trying to gain muscle, maintain performance or reduce body weight? Are they recovering between sessions, or are fatigue and discomfort gradually accumulating?

I'd then look at their ordinary eating pattern, total energy intake, approximate protein and carbohydrate intake, food variety and whether meals are arranged in a way that suits their routine.

A detailed supplement review can follow, but I'd prefer to know whether the diet is adequate before looking for additional products.

There's also a tendency to attribute progress or lack of progress to individual nutrients when the explanation may involve several interacting factors. Poor performance doesn't automatically mean more carbohydrates are required. Persistent soreness doesn't prove inadequate protein. Fatigue doesn't establish a vitamin deficiency.

Research helps us understand what might be happening, but it doesn't remove the need to consider the individual.

Our discussion of biochemical individuality explores some of the biological variation influencing responses to diet and other interventions. Individual variation is real, although it shouldn't become a reason to disregard established nutritional principles.

In many cases, I'd rather see someone make a small, well-reasoned change to their diet and assess how they respond than introduce several new strategies at once. It's difficult to learn much from an intervention when everything changes simultaneously.

That might mean adjusting food intake during a particularly demanding training block, changing meal timing before a prolonged session or ensuring sufficient recovery between workouts.

If symptoms persist or raise concerns about health, dietary experimentation isn't a substitute for appropriate medical assessment.

Final thoughts

The fundamentals of sports nutrition are reasonably well established, but applying them becomes more involved as training demands increase.

Adequate energy remains the starting point. Protein intake should be sufficient for the training and the individual, while carbohydrate availability becomes particularly relevant when exercise is prolonged, frequent or heavily dependent on glycogen. Dietary fats contribute essential nutrients, and hydration requirements need to reflect actual conditions and fluid losses.

There are areas where the evidence is strong enough to support practical recommendations, alongside others where individual variation and limitations in the research warrant more caution.

I wouldn't approach nutrition as a set of numbers that must be increased every time training becomes harder. Nor would I assume that a previously successful diet will remain appropriate when the training programme changes substantially.

It's more useful to review food intake as part of the overall training process, making adjustments when the workload, recovery demands or individual circumstances provide a reason to do so.

In Part 2, I'll look more closely at applying these principles: how to arrange food intake around different training days, when carbohydrate timing becomes useful, how to approach demanding periods of training and what recovery nutrition looks like outside textbook examples.

Research and further reading

1. Mountjoy M, et al. (2023). 2023 International Olympic Committee's consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 57, 1073–1097. https://doi.org/10.1136/bjsports-2023-106994. Read alongside the journal's published correction.

2. Jäger R, et al. (2017). International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14, 20. https://doi.org/10.1186/s12970-017-0177-8

3. Thomas DT, Erdman KA, Burke LM. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116, 501–528. https://doi.org/10.1016/j.jand.2015.12.006

4. Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(S1), S17–S27. https://doi.org/10.1080/02640414.2011.585473

5. Sawka MN, et al. (2007). American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39, 377–390. https://doi.org/10.1249/mss.0b013e31802ca597

6. NHS. Vitamin D — Vitamins and minerals. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/

Written by

Chris Simon (Founder, One Life Foods)

Chris has worked in the supplement industry since 2009, with a particular interest in ingredient sourcing, product quality and formulation. Through One Life Foods, he aims to make supplement information more transparent and evidence-led, particularly in areas where scientific findings are frequently simplified in marketing.

Read more about Chris and One Life Foods.

Disclaimer

This article is for general educational purposes and isn't intended to provide individual medical or dietary advice. Nutritional requirements vary according to training demands, age, health status and other personal circumstances. Anyone experiencing persistent fatigue, suspected nutrient deficiencies, menstrual disturbances, unexplained symptoms or concerns around restrictive eating should seek advice from an appropriately qualified healthcare professional or registered dietitian. Food supplements shouldn't be used as a substitute for a varied, balanced diet and healthy lifestyle.