Nutrition for Health and Exercise

The UK healthy eating model is the reference point for population dietary advice, and it describes proportions rather than prescribing meals.

It divides food into five groups: fruit and vegetables; potatoes, bread, rice, pasta and other starchy carbohydrates; dairy and alternatives; beans, pulses, fish, eggs, meat and other proteins; and oils and spreads. Fruit and vegetables and starchy carbohydrates each make up just over a third of what is eaten. Foods high in fat, salt and sugar sit outside the model as non-essential. The proportions apply across a day or a week rather than to every meal, which is a useful thing to say to patients who assume otherwise.

Several specifics recur. At least five portions of a variety of fruit and vegetables a day, with fruit juice and smoothies limited to a combined 150 mL because of free sugars. Two portions of fish a week, one of them oily. Higher fibre and wholegrain versions of starchy foods, with a fibre recommendation of 30 g a day, which the great majority of UK adults do not meet according to the most recent national diet and nutrition survey. Six to eight glasses of fluid a day, including water, lower fat milk and unsweetened tea and coffee. The model was revised following the Scientific Advisory Committee on Nutrition (SACN) review of carbohydrates and health, which drove the reduction in free sugars and the increased emphasis on fibre and wholegrains.

Fat and carbohydrate both fuel exercise, and the balance between them shifts predictably with intensity.

At low intensity, fat oxidation supplies most of the energy, and body fat stores are large relative to glycogen stores, although the rate at which fat can supply energy is limited. As intensity rises, the contribution from carbohydrate increases and eventually predominates, because carbohydrate can be broken down faster and can be used anaerobically. Both fuels contribute across most intensities, so neither switches off when the other predominates, and the balance also depends on duration, training status, recent carbohydrate availability, glycogen stores and metabolic health. Muscle and liver glycogen stores are limited, which is why carbohydrate availability becomes limiting in prolonged or intense exercise while fat availability does not. Metabolic flexibility, the ability to switch efficiently between fuels, improves with training and is impaired in insulin resistance.

This is where sports nutrition guidance departs from population guidance, and the two should not be confused: the figures that follow are training-load-specific and form no part of the UK healthy eating model. Carbohydrate guidance runs from roughly 3 to 5 g/kg body mass a day for low-volume or skill-based training, through about 5 to 7 g/kg for moderate training of around an hour daily, to 6 to 10 g/kg for endurance training of one to three hours daily, and up to 8 to 12 g/kg for extreme endurance loads. Requirements are better periodised to the actual session than assigned from a single weekly label, and for most recreationally active people food-based guidance and adequate total energy are more useful than prescribing exact grams per kilogram.

Protein works the same way. The UK population reference nutrient intake is age and sex specific and equates to roughly 0.75 g/kg a day in healthy adults. Older adults are commonly advised around 1.0 to 1.2 g/kg where clinically appropriate, because of anabolic resistance. Exercising people commonly require approximately 1.2 to 2.0 g/kg depending on training goal, energy availability and health status. Rather than a fixed post-session amount, a practical per-meal target is around 0.25 to 0.4 g/kg of high-quality protein distributed across the day, with older adults at the upper end. Total daily intake and adequate energy availability matter more than a narrow post-exercise window.

Several groups need the general advice modified. Older adults require relatively more protein than younger adults to achieve the same muscle protein synthesis, because of anabolic resistance, and combining adequate protein with resistance training is more effective than either alone for preserving muscle. People taking glucagon-like peptide-1 agonists lose muscle as well as fat, so protein intake and resistance training both matter particularly, and appetite suppression can make reaching protein targets genuinely difficult. In chronic kidney disease, protein recommendations are individualised and specialist dietetic input is needed rather than a generic instruction to eat more. In diabetes, carbohydrate around exercise interacts directly with insulin and sulfonylurea dosing.

Vegetarian and vegan diets support both health and performance, with attention to protein quantity and distribution, and to iron, vitamin B12, vitamin D, calcium, iodine, zinc and omega-3 fatty acids. Iron deserves emphasis because low iron stores may contribute to fatigue, impaired training capacity and reduced performance before anaemia develops, particularly in menstruating women and endurance athletes. Deficiency should be confirmed and its cause investigated rather than supplementing on risk status alone. On vitamin D, UK advice is that everyone should consider a daily supplement of 10 micrograms during autumn and winter, given limited sunlight at UK latitude, and that people with limited sun exposure or darker skin should consider it throughout the year.

A major clinical risk in exercising populations is not suboptimal macronutrient timing but simply not eating enough to support both training and normal physiological function. Problematic low energy availability, meaning sustained rather than short-term adaptable exposure, drives relative energy deficiency in sport, with consequences spanning bone health, endocrine and menstrual function, immunity, cardiovascular and gastrointestinal health, mood and performance. It affects men and women, and it occurs both through deliberate restriction and inadvertently through increased training without a matching increase in intake.

Two practical implications follow. Any conversation about diet with an exercising person should establish whether intake has kept pace with training before discussing anything more refined. And nutritional advice in this setting carries real risk of harm if framed around body shape or restriction, particularly in young people, so the framing should be fuelling for health and performance rather than weight or physique. Where disordered eating is suspected, that becomes the clinical priority and specialist input is needed. The dedicated StudySEM pages on relative energy deficiency in sport and on eating disorders cover this ground in detail and should be the reference point rather than a nutrition consultation alone.

• •The UK healthy eating model describes proportions across a day or week, not every meal, with fruit and vegetables and starchy carbohydrates each just over a third.
• •Fibre recommendation is 30 g a day, which most UK adults do not meet; fruit juice and smoothies are capped at a combined 150 mL.
• •Fat predominates as fuel at low intensity and carbohydrate at higher intensity, so carbohydrate needs scale with training load.
• •Sports carbohydrate guidance runs from about 3 to 5 g/kg for light training to 6 to 10 g/kg for one to three hours daily, separate from population guidance.
• •The UK population protein reference is around 0.75 g/kg; exercising people commonly need about 1.2 to 2.0 g/kg depending on goal.
• •Inadequate total energy matters more than macronutrient detail, and framing advice around physique risks harm.