Eating in the Off-Season: Matching Fuel to Lower Training Without Under-Fuelling

The end of the season changes almost everything about a triathlete's week. Long rides become short turbo sessions, run volume drops, and there may be a few weeks of very little structured training at all. Food often doesn't change in step. Some athletes keep eating as if they were still training for an Ironman. Others decide that winter is the time to "tidy up" their diet and eat as little as possible until spring.

This article is about the second risk. It covers what energy availability is, why the off-season isn't a safe time to under-fuel, what the research says about meal timing and appetite, and how to match fuel to lighter training without restriction. It deliberately contains no calorie, macronutrient-gram, weight or body-composition targets. If you want individual advice, a registered sports dietitian is the right person to ask.

What energy availability means

Energy availability is the energy left for the rest of your body's functions after the energy cost of exercise has been paid. A 2021 review by Areta, Taylor and Koehler in the European Journal of Applied Physiology defined it as "the amount of dietary energy available to sustain physiological function after subtracting the energetic cost of exercise."

Low energy availability (LEA) can come from training more, eating less, or both. The review described it as a potent disruptor of the hormonal system, linked to problems with reproductive function, metabolism, bone and muscle. Two points from the review are important here:

• Most of the evidence is cross-sectional, comparing athletes at one point in time. Studies that actually change energy availability are small and usually last five days or less.
• The concept was developed in women, and experimental evidence in men is still limited.

TriForward's "Under-Fuelled, Not Undertrained" covers LEA in age-group triathletes in more detail.

REDs: the 2023 consensus

The 2023 IOC consensus statement on Relative Energy Deficiency in Sport (REDs), led by Mountjoy and published in the British Journal of Sports Medicine, described REDs as a syndrome of harmful health and performance outcomes in athletes exposed to LEA. Key points:

• It affects female and male athletes.
• Not all LEA is equally harmful. The consensus model distinguishes adaptable from problematic LEA exposure, with individual factors influencing the outcome.
• It introduced a clinical assessment tool (REDs CAT2) to help clinicians detect and diagnose REDs based on accumulated signs and risk.

Inference: brief, mild exposure is likely to sit at the adaptable end. A few days of eating less than you use, such as after a race or during a busy week, is not a medical problem in itself. Weeks or months of deliberately eating too little is where the risk lies, and an off-season diet is exactly that.

Why the off-season isn't a safe time to under-fuel

It's tempting to think LEA only matters when training is heavy. But energy availability depends on what you eat as well as what you burn. If you cut food faster than you cut training, availability can fall even when training is light.

There's also a recovery argument. Many triathletes end the season after months of high training, racing and travel. Inference: the off-season is when hormones, bone and immune function have the chance to recover from that, and restricting food during this window may remove the opportunity.

What LEA does to bone

Bone is one of the best-documented casualties.

A 2018 study by Heikura and colleagues in the International Journal of Sport Nutrition and Exercise Metabolism studied national and world-class female and male distance athletes.

• In women, bone injuries were about 4.5 times more common in 13 amenorrhoeic athletes, whose periods had stopped, than in 22 with regular cycles.
• In men, bone injuries were also more common in 10 athletes with low testosterone than in 14 with normal levels.
• Athletes flagged as higher-risk by REDs and Female Athlete Triad screening tools had more fractures over their careers and more days lost to injury.

The authors also found that calculating energy availability from food and training diaries was difficult and error-prone. They concluded that hormonal and menstrual markers gave a more objective picture. That's a useful lesson for age-groupers: counting food intake isn't a reliable way to tell whether you're under-fuelled.

Male cyclists

A 2018 study by Keay, Francis and Hind in BMJ Open Sport & Exercise Medicine assessed 50 competitive male road cyclists using a sport-specific questionnaire and clinical interview, bone scans and blood tests.

• 28% had low energy availability.
• 44% had low bone density at the lumbar spine.
• The 10 cyclists with chronic LEA had lower testosterone than those with adequate energy availability.
• Cyclists with LEA who had no history of load-bearing sport had the lowest bone density.

This was a cross-sectional study of men who mostly cycle, not triathletes, but it shows LEA is not only a women's issue and that endurance athletes who do little impact training have less margin for error. TriForward's "Lifting for Bone" covers the loading side.

It's not just how much, but when

One of the more useful findings for age-groupers is that the pattern of eating across the day appears to matter, not only the daily total.

Female endurance athletes

A 2018 study by Fahrenholtz and colleagues in the Scandinavian Journal of Medicine and Science in Sports reanalysed seven-day food and training records from 25 elite female endurance athletes: 10 with regular periods and 15 with menstrual dysfunction.

• Their 24-hour energy availability didn't differ significantly between groups.
• But the athletes with menstrual dysfunction spent more hours of each day in an energy deficit, calculated hour by hour.
• More hours in deficit were associated with a lower resting metabolic rate relative to predicted, lower oestradiol and higher cortisol.

Male endurance athletes, including triathletes

A 2018 study by Torstveit and colleagues in the International Journal of Sport Nutrition and Exercise Metabolism applied a similar method to 31 male cyclists, triathletes and long-distance runners from regional clubs. Twenty had a suppressed resting metabolic rate, a recognised sign of energy deficiency, and 11 had a normal one.

• 24-hour energy availability didn't differ between the groups.
• The suppressed group spent more hours in a large deficit across the day.
• Larger deficits were associated with higher cortisol and a lower testosterone-to-cortisol ratio.

Both studies are cross-sectional and small, so they can't prove that long gaps between meals cause problems. But they point the same way, in women and men. Inference: skipping breakfast before a session, training through lunch and then eating most of your food in the evening may matter, even if the day's total looks adequate. That pattern is common in age-groupers who train before or after work.

Why hunger isn't a reliable guide

Many athletes expect appetite to adjust automatically: eat more when training more, less when training less. The evidence suggests it isn't that simple.

A 2013 meta-analysis by Schubert and colleagues in Appetite pooled 29 studies with 51 trials of a single exercise bout lasting 30 to 120 minutes. Exercise had a trivial effect on how much people ate in the hours afterwards. Because they didn't eat more to compensate, a session produced a short-term energy deficit, although responses varied between individuals.

These were single sessions in mostly non-athletes, so they say nothing direct about the off-season. Inference: appetite doesn't track training closely in either direction. During heavy training, hunger may not prompt you to eat enough, which is one route to LEA. When training drops, appetite may take time to settle. Neither is a reason to override hunger with restriction. It's a reason to rely on regular meals and planned fuelling around sessions rather than on hunger alone.

Matching fuel to lighter training

The idea of "fuel for the work required", set out by Impey and colleagues in a 2018 review in Sports Medicine, is that carbohydrate availability should be adjusted to the demands of upcoming sessions. It was written as a framework for planning carbohydrate around harder and easier sessions, including some deliberately low-carbohydrate ones, not as a case for eating less overall. TriForward's "Train Low, Race High — And Probably Don't" explains why deliberate low-carbohydrate training is a specialist tool with real risks.

Applied to the off-season, the principle is straightforward. The main thing that changes when training drops is the fuel needed for and around sessions, not the food your body needs for everything else. The following suggestions are inference from the evidence above, not a tested plan:

1. Scale the fuel around sessions to the session. A short, easy turbo needs less fuelling around it than a long ride, and a gym session less than a race-pace brick. TriForward's "Do You Need Carbs on a 60-Minute Turbo Session?" covers the short-session question.
2. Keep regular meals. Three meals and snacks spread across the day, with no long gaps, is consistent with what the within-day studies suggest.
3. Don't train fasted out of habit. An easy session before breakfast now and then is fine for many people, but a pattern of fasted training followed by a long gap to lunch builds hours of deficit.
4. Eat after sessions, especially strength sessions. The off-season strength block still needs recovery nutrition. TriForward's "Protein for the Lifting Triathlete" covers protein.
5. Keep variety. Fruit, vegetables, whole grains, dairy or alternatives and protein-rich foods support iron, calcium and vitamin D status. See TriForward's "Iron and the Triathlete" and "Vitamin D in Winter: Who Needs It and What It Won't Do for Performance".
6. Don't count your way there. The Heikura study found diet diaries an unreliable way to judge energy availability. Signs and symptoms are more useful.

The 2016 position stand on nutrition and athletic performance by Thomas, Erdman and Burke, from the American College of Sports Medicine and North American dietetics organisations, recommended referring athletes to a registered dietitian for a personalised plan. If you want to change how you eat this winter, that's the place to start.

Warning signs to watch for

Commonly described signs of low energy availability, several of which appear in the studies above, include:

• Missed, irregular or absent periods, in women not taking hormonal contraception that masks them.
• Low libido or loss of morning erections in men.
• A bone stress injury, particularly with no obvious training error.
• Frequent illness, persistent fatigue or feeling cold much of the time.
• Performance stalling or dropping despite rest.
• Preoccupation with food, guilt about eating, or feeling that food must be earned through training.

Any of these deserves a conversation with a doctor or sports dietitian. They don't prove you have REDs, but they shouldn't be ignored.

A triathlon scenario

The following example is illustrative, not drawn from a study. A 42-year-old triathlete finishes her season in September. She decides to use the winter to "clean up" her eating, skips breakfast before her morning swims and runs, has a small lunch and makes up the rest in the evening. By January her periods have become irregular, she has had three colds and her run has felt flat for weeks.

A better approach, based on the evidence above, might be:

• Eat breakfast before or straight after morning sessions, rather than training fasted and waiting until lunch.
• Keep fuelling around key sessions, such as the weekly long ride and her strength sessions, while scaling it back for short easy ones.
• Keep regular meals and snacks so she isn't spending most of the day in a deficit.
• See her GP about the irregular periods, rather than assuming they're a normal effect of training.

Common mistakes

• Treating winter as the time to diet, when the body may still be recovering from the season.
• Cutting food faster than training, which lowers energy availability even when training is light.
• Long gaps around sessions, especially fasted morning sessions followed by a late lunch.
• Relying on hunger alone, which doesn't track training changes closely.
• Assuming LEA is a women's issue. The male cyclist and male endurance athlete studies show otherwise.
• Ignoring early signs such as menstrual changes, low libido or repeated illness.

What we don't know

• Off-season eating in triathletes. No studies have looked at how age-group triathletes eat in the off-season or how that affects their health.
• How much LEA is too much. The consensus distinguishes adaptable from problematic LEA, but the boundary varies between individuals.
• Within-day timing. The hour-by-hour studies are small and cross-sectional, so they show associations, not cause and effect.
• Masters athletes. Most of the evidence comes from younger elite or competitive athletes.
• How quickly the body recovers once energy availability is restored, and whether the off-season is long enough.

References

• Areta JL, Taylor HL, Koehler K. Low energy availability: history, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males. European Journal of Applied Physiology, 2021;121(1):1–21. doi:10.1007/s00421-020-04516-0
• Mountjoy M, Ackerman KE, Bailey DM, Burke LM, Constantini N, Hackney AC, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 2023;57(17):1073–1098. doi:10.1136/bjsports-2023-106994
• Heikura IA, Uusitalo ALT, Stellingwerff T, Bergland D, Mero AA, Burke LM. Low energy availability is difficult to assess but outcomes have large impact on bone injury rates in elite distance athletes. International Journal of Sport Nutrition and Exercise Metabolism, 2018;28(4):403–411. doi:10.1123/ijsnem.2017-0313
• Keay N, Francis G, Hind K. Low energy availability assessed by a sport-specific questionnaire and clinical interview indicative of bone health, endocrine profile and cycling performance in competitive male cyclists. BMJ Open Sport & Exercise Medicine, 2018;4(1):e000424. doi:10.1136/bmjsem-2018-000424
• Fahrenholtz IL, Sjödin A, Benardot D, Tornberg Å, Skouby S, Faber J, Sundgot-Borgen JK, Melin AK. Within-day energy deficiency and reproductive function in female endurance athletes. Scandinavian Journal of Medicine and Science in Sports, 2018;28(3):1139–1146. doi:10.1111/sms.13030
• Torstveit MK, Fahrenholtz I, Stenqvist TB, Sylta Ø, Melin A. Within-day energy deficiency and metabolic perturbation in male endurance athletes. International Journal of Sport Nutrition and Exercise Metabolism, 2018;28(4):419–427. doi:10.1123/ijsnem.2017-0337
• Schubert MM, Desbrow B, Sabapathy S, Leveritt M. Acute exercise and subsequent energy intake: a meta-analysis. Appetite, 2013;63:92–104. doi:10.1016/j.appet.2012.12.010
• Impey SG, Hearris MA, Hammond KM, Bartlett JD, Louis J, Close GL, Morton JP. Fuel for the work required: a theoretical framework for carbohydrate periodization and the glycogen threshold hypothesis. Sports Medicine, 2018;48(5):1031–1048. doi:10.1007/s40279-018-0867-7
• Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and athletic performance. Medicine & Science in Sports & Exercise, 2016;48(3):543–568. doi:10.1249/MSS.0000000000000852