Under-fuelling can have a serious effect on your health and performance. The problem is many athletes and regular exercisers are eating less than they realise. What starts as a genuine desire to shed a few pounds or get fitter can easily backfire and result in under-fuelling. This means that day after day, week after week, you are not eating enough to meet your energy needs. Instead of getting fitter and faster you can end up fatigued and illness-prone. As many athletes (and here and here) have discovered, under fuelling can also cost you your performance.
Who is at risk?
Athletes most at risk include those involved in sports where havinga high power-to-weight ratio confers an advantage (such as running and cycling), weight category sports (such as boxing), and aesthetic sports (such as bodybuilding, dance and gymnastics). Young athletes can be especially vulnerable to restrictive eating and subsequent under-fuelling.
What is under-fuelling?
Under fuelling or, more accurately, low energy availability (LEA) refers to the situation in which your energy intake does not match the fuel demands of your training and basic body functions. As described in my previous article, LEA can happen either intentionally when you cut your energy intake to lose weight or unintentionally when you increase your training load without adequately increasing your food intake.
LEA underpins a condition called relative energy deficiency in sport (RED-S), which more accurately describes the clinical syndrome previously known as the female athlete triad. Although more common in females, RED-S is also something that affects male athletes.
What does energy availability mean?
Energy availability (EA) the amount of energy left over and available to the body to carry out essential functions after the energy cost of exercise has been subtracted from the energy you take in from food. In other words:
Energy Intake – Exercise Energy Expenditure = Energy Availability
For example, a 70kg athlete with 15% body fat who consumes 2500 kcal a day and burns 1000 kcal training has an energy balance of 1500 kcal. If you divide this by the athlete’s fat-free mass (FFM) (55kg) and you have an EA of 27 kcal/ kg FFM/ day. For optimal health and performance, EA should be about 45 kcal/ kg FFM/ day, although the threshold varies between individuals. Going below this level (particularly below 30 kcal/ kg/ FFM/ day) results in LEA and means you will not have enough energy available to cover basic physiologic demands. Your body will go into ‘energy-saving mode’, reducing its metabolic rate and essential functions.
What are the risks of under-fuelling?
Under-fuelling over weeks or months results in negative health and performance effects. It can impair hormonal function, immune function, gastrointestinal function, cardiovascular function and psychological function. In the longer-term, health problems such as infertility, low bone mineral density, nutrient deficiencies and disordered eating can develop (Fig 1). Even short-term energy deficits, for example during a long workout or not consuming anything following a workout, have been shown to disrupt hormones. Long-term LEA can reduce your performance and increase your risk of illness and injury (Fig 2).
How do you know if you are under-fuelling?
There are several early warning signs to look out for. These include
missed or irregular periods in females (although this can be masked by oral contraception)
lack of morning erection in males
persistent fatigue
a drop in performance or lack of expected improvement in performance
poor recovery
increased perception of effort during exercise and daily activities
recurrent illness and injuries (such as stress fractures)
changes in mood (such as feeling anxious or irritable)
reduced social interaction
problematic relationship with food and/ or training
disrupted sleep patterns.
How to prevent under-fuelling
Contrary to popular belief, lighter does not always mean faster! The weight at which you perform at your best will depend on many factors, including your age, gender, genetics and natural build. Instead of trying to get super lean, aim instead to achieve a healthy weight and body composition that allows you to perform well without compromising your health.
If you really do need to drop a few pounds, then reduce your current calorie intake byapproximately 15% on some training days, but not others. This should produce a relatively modest energy deficit of around 300 calories a day. Any more than this risks under fuelling and LEA. Calculating your personal energy requirements can be a useful starting point and there are a number of food tracking apps that you can use.
Under-fuelling can begin unintentionally so if you have recently increased training volume or if you are doing a hard block of training, you should take steps to avoid it by being more proactive in planning your food. Pay attention to your energy levels, and make a sustained, conscious effort to consume enough energy (calories). You will need to eat more on hard training days. If this proves difficult, then including some lower fibre (e.g. ‘white’ instead of wholemeal pasta) options can make this easier. Include plenty of foods rich in healthy fats, such as nuts, seeds, nut butters, avocado and olive and rapeseed oil in all your meals and snacks. These foods will help boost your energy intake without adding too much extra volume. If you find it difficult to eat larger portions, add high-energy snacks, such as nuts, nut butter on toast, and fruit and nut bars between meals.
If you suspect under-fuelling, then you will need to increase your food intake and/ or reduce your training volume. However, these two things can often be harder than they sound so consider seeking the help of a professional to get you back on track. Your GP, sports doctor, sports dietitian, or a psychologist will be able to provide assessment and advice. My previous article also provides practical advice for those with amenorrhoea.
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Expert advice on how to how to eat well and improve your performance
One of the most common questions I get asked by runners is why they can’t lose weight despite running regularly. Some runners find that they actually gain weight; a phenomenon dubbed ‘marathon weight gain’. Although this may seem counterintuitive, it is also very frustrating for those aiming to lose weight. But there are a number of explanations, which may help you understand why you may not be losing weight.
Its all too easy to overestimate how many calories you’re burning running and overcompensate by eating too many calories. The truth is you may not be burning as many calories as you think. For example, if you weigh 60kg and run for 30 minutes three times a week, you’re burning 933 kcal. That’s equivalent to weight loss of less than 0.2kg, barely enough to register on the scales. You’ll need to create a deficit of 7,700 kcal to lose 1kg.
When you’re running regularly, it’s tempting to see a workout as a free pass to eat what you like, and easy to over consume treats. A couple of biscuits with your morning coffee? Another slice of cake? Why not – after all you just did a long run. But all those extra calories here and there can soon add up if you’re not mindful of your food intake. Unless you’re blessed with a fast metabolism or an ability to self-regulate your appetite, you may need to keep a more careful check on portion sizes and daily calories. If you want to lose weight running, you’ll need to consume fewer calories than you’re burning.
You may be very active while you run but do you then sit for long periods during the day? Many people may not be aware of it but, on days when they run, they tend to do less spontaneous activity, like walking or just getting up from their chair and moving around (known catchily as ‘non-exercise activity thermogenesis’ or NEAT). This means you could be burning fewer calories throughout the day, and so your overall daily burn may not be much different from what it was before you took up running. A study in 2015 found that people who exercised vigorously but sat most of the time were 1.65 times more likely to develop metabolic syndrome – type 2 diabetes, high blood pressure and obesity.
Do you consume too many sports nutrition products? Energy gels, bars and drinks contain a lot more calories than many people realise. A 500ml bottle of sports drink typically contains 140 calories; a gel 90 calories and a bar 200 calories. It’s easy to get sucked into the hype around these products but unless you’re exercising for longer than 90 minutes you don’t need extra carbohydrate during your run. You should have enough fuel (glycogen) in your muscles to keep you going to the end of your workout.
Here are 6 tips on how to avoid running weight gain
Be realistic about how many calories you are burning during a run – activity trackers and heart-rate monitors can give you a reasonable idea (although, being based on predictive equations and standard algorithms, they are not super accurate).
Be honest about your food intake – it can be helpful to log your food intake with an app such as MyFitness Pal (or just write everything down) for a few days.
Sit less – Try to incorporate more movement into your daily routine and break up long periods of sitting with short walks or pacing while talking on the phone.
Schedule your workout just before a main meal – this does away with the requirement for a post-run snack, and means you won’t be ravenous before your meal (leaving too long a gap can make you feel more hungry).
Don’t reward your workout with unhealthy snacks– refuel instead with nutrient-rich foods like milk, yogurt, nuts, fruit and veg
Save sports drinks, gels and bars for your long runs (more than 90 minutes)
In summary, running regularly has countless health benefits but, unless you also look at what you’re eating, it won’t automatically result in weight loss. It’s easy to overestimate your energy needs and overeat. If you want to lose weight running, you’ll need to consume fewer calories than you’re burning (about 10 – 15% less than before) and that means choosing nutrient-rich foods over calorie-dense snacks.
If you enjoyed this post and want to find out more about sports nutrition, then check out my latest book, The Runner’s Cookbook. It features more than 100 delicious recipes to fuel your running. With a foreword from five-time Olympian Jo Pavey, the book also provides practical nutrition advice on fuelling before, during and after running, guidance on hydration and supplements, weight loss tips, how to recover from injury, and how to prepare for 5k, 10k, half marathons, marathons and ultra races.
Do you exercise to lose fat? You’re not alone – getting lean is a major goal for many people who exercise regularly. But attaining a very low body fat percentage – or a level that is unnaturally low for your genetic make-up – carries big health risks. What most people don’t know is that cutting body fat too rapidly or too severely can wreak havoc with your hormones and result in missed periods (amenorrhoea), reduced fertility and weakened bones.
In a study of regular exercisers, half of the women were found to have subtle menstrual hormone disruption. A third had no periods at all. While the idea of not having the hassle of periods each month may sound appealing, it’s important to understand that this is not healthy! All women of reproductive age, whether an athlete or not, should have regular periods, otherwise there are potential serious health and performance consequences.
It’s all down to a concept called low energy availability (EA). This is the amount of energy available to the body to perform all its essential functions after exercise expenditure is subtracted (i.e. energy intake minus exercise energy expenditure). When this drops too low – either by intentionally or unintentionally restricting energy intake below the level required to meet demand or by increasing your training volume without a corresponding increase in fuel intake – then your body goes into deficit and your periods can stop. In healthy adults, a value of 45 kcal/kg fat-free mass /day equates with energy balance and optimum health.
Amenorrhoea is one of the most obvious external symptoms of Relative Energy Deficiency in Sport (RED-S), defined as a mismatch between your food intake and the energy demands of your body. RED-S developed from the concept of the Female Athlete Triad (relationship between three inter-related components: energy availability, menstrual function and bone health) when it became apparent that low EA had multiple effects on health and performance, and also affects men. In men, it can lead to a drop in testosterone levels.
Researchers believe RED-S is caused by low energy availability but a combination of many lifestyle-related factors are often involved, including stress, poor sleep and rapid weight loss. Doctors sometimes call it lifestyle-induced amenorrhoea or functional hypothalamic amenorrhoea.
Why do periods stop? It has been suggested that it’s an energy-conserving adaptation by the body. When there is insufficient energy available, the body goes into an energy saving mode. The body fat threshold that triggers hormonal disruption and amenorrhoea varies from one person to the next – but is thought to be between 17 and 22%.
The body mechanism is as follows: low energy availability increases cortisol production by the adrenal glands, which disrupts the release of gonadotrophin-releasing hormone (GnRH) from the brain. This, in turn, reduces the production of luteinising hormone (LH), follicle-stimulating hormone (FSH), oestrogen and progesterone, and stops you having periods.
One of the most severe health effects of this hormone disruption is the reduction in bone density and increased risk of early osteoporosis and stress fractures. Oestrogen and progesterone both act directly on bone cells to maintain bone turnover, so when levels drop, the breakdown of old bone exceeds the speed of formation of new bone. The result is loss of bone minerals and a loss of bone density. In men, low testosterone has a similar effect on bones and causes bone mineral loss.
RED-S can severely disrupt your fertility (thus reducing your chances of getting pregnant), slow your metabolic rate, impair immunity, increase fatigue and affect cardiovascular and gut health. Thyroid hormone, growth hormone and IGF-1, are also severely reduced.
RED-S also results in many performance-hindering effects. These include an increased risk of soft tissue injuries, stress fractures, decreased strength and endurance, prolonged healing of injuries and reduced ability to recover from hard training sessions.
However, the good news is that once your body fat level increases over a certain threshold and your training volume is reduced, your hormonal balance, periods and fertility generally return to normal. Studies show that when amenorrhoeic athletes improve their diet and restructure their training programme to improve energy balance, normal menstruation resumes within a few months (depending on the severity of the energy deficiency and the duration of amenorrhoea) and performance improves consistently. This is perhaps the most persuasive reason to seek treatment if you have amenorrhoea.
Practical advice
You should definitely seek advice if you have suffered amenorrhoea for longer than 6 months. An initial consultation with your GP will rule out medical causes of amenorrhoea, such as polycystic ovary syndrome. You should then get a referral to a specialist, such as an endocrinologist or sports medicine doctor.
Treatment will centre on increasing energy availability and restoring ‘normal’ body weight and body fat. This usually means increasing your food intake (usually by 300 – 600 kcal a day) and you may be advised to reduce your training frequency, volume and intensity, incorporate periodisation to your current programme or include more recovery.
As well as energy intake, focus on improving the nutritional quality of your food intake to ensure you’re meeting your macronutrient and micronutrient needs. Consult a registered dietitian (RD) or registered nutritionist (RNutr) if you would like more detailed advice.
Avoid any diet that eliminates entire food groups or centres around a set of strict rules – restrictive eating plans are likely to be deficient in nutrients that you need for proper endocrine functioning and may lead to unhealthy obsession with food. If you suspect a food allergy or intolerance, seek a medical diagnosis and professional guidance. Do not self-diagnose or use high street or home test kits.
Focus on your recovery nutrition – replenishing energy and consuming sufficient protein after training sessions are key for the prevention and treatment of RED-S.
If you enjoyed this post and want to find out more about sports nutrition, then check out the new edition of The Complete Guide to Sports Nutrition , the definitive practical handbook for anyone wanting a performance advantage. It’s the 8th edition (the 1st edition came out in 1993!) and it has been fully updated and revised to bring together the latest research and information on sport and exercise nutrition. It covers topics such as
Maximizing endurance, strength and performance
Carbohydrate, protein and fat requirements
Sports supplements
Improving body composition
Eating plans to cut body fat, gain muscle and prepare for competition
While a healthy diet is central to optimal performance, for some athletes the quest to eat only the ‘right’ foods can morph into orthorexia, an unhealthy fixation with ‘eating correctly’. What starts as a health kick or desire to shed surplus pounds can spiral into obsessive behaviour. One recent study suggests that as many as 28% of athletes are affected by orthorexia.
If you have ever experienced extreme anxiety after eating a slice of cake, declined a dinner invitation for fear of its impact on your training gains or had to exercise after eating a certain food because you felt so guilty, then you may be affected by orthorexia.
You’re probably familiar with the more commonly known eating disorders, anorexia nervosa and bulimia nervosa, but most people don’t know about another serious eating disorder: orthorexia. It is not defined simply by weight loss or eating too little but rather by an obsession with healthy eating. It differs from anorexia nervosa in that the goal isn’t necessarily thinness or limiting calories but a desire to be pure, clean and healthy.
A defining feature of orthorexia is an obsessive adherence to an increasingly restrictive ‘clean’ diet. Sufferers have a strong desire to maximise their health and will focus on food ‘quality’ and ‘purity’, rather than calories. They have an intense fear of eating anything perceived as unhealthy or ‘unclean’.
Blurred lines
Many athletes weigh their food religiously, track their macros and adhere to self-imposed food rules. However, such strict control can often mask a dysfunctional relationship with food.
Today it is trendy to ‘eat clean’, that is, to follow a ‘food lifestyle’ like low-carb, paleo or vegan. On the surface this seems harmless but it can easily mask an obsession with food. The problem is, in sports where body weight is closely linked to performance, there’s a blurred line between healthy eating and unhealthy obsession.
Unhealthy obsession
Some people are more vulnerable than others. One study published in Eating and Weight Disorders Journal in 2017 found that people with higher orthorexia tendencies scored more highly for body dissatisfaction and perfectionism.
Of course, just because you’ve decided to ‘eat clean’ doesn’t mean you have orthorexia. Problems arise when your eating becomes increasingly restrictive and starts to negatively impact your social life, relationships, self-worth, happiness and wellbeing.
Social Media to blame?
Some blame the rise of social media celebrities who, despite no formal training in nutrition, espouse an ‘eat like me, look like me’ approach. The ‘clean eating’ movement encourages restriction and self-prescribed ‘good’ and ‘bad’ foods. Research published in 2017 found a strong correlation between time people spent on Instagram and symptoms of orthorexia.
Warning signs and symptoms of orthorexia
Compulsive checking of ingredient lists and nutrition labels
Cutting out an increasing number of foods (e.g. sugar, carbs, dairy)
Eating only foods that are deemed ‘healthy’ or ‘pure’
Afraid to eat anything ‘unhealthy’
Refusing to eat foods that you don’t know what’s in them or how they were prepared
How to maintain a healthy relationship with food
Identify your triggers e.g. social media and unfollow people who make you feel bad.
Resist the temptation to compare on social media
Spend less time reading health news – it may do more harm than good
Don’t live in a bubble – spend time with people outside of your sport, with other interests
Food should not make you scared or anxious – it’s something to be enjoyed and celebrated!
If you enjoyed this post and want to find out more about sports nutrition, then check out my brand new book, The Runner’s Cookbook. It features more than 100 delicious recipes to fuel your running. With a foreword from five-time Olympian Jo Pavey, the book also provides practical nutrition advice on fuelling before, during and after running, guidance on hydration and supplements, weight loss tips, how to recover from injury, and how to prepare for 5k, 10k, half marathons, marathons and ultra races.
One of the most frequent questions I get asked by runners after a talk is how to prevent or cope with gastro-intestinal (GI) problems and transit troubles during training and races. It’s not an issue many like to talk about openly but it’s one that’s surprisingly common among endurance athletes.
It is estimated that 30 to 50% of endurance athletes experience GI problems related to exercise. The most debilitating and annoying of these GI issues? The sudden and overwhelming need to evacuate your bowels. In cases of extreme frequency or discomfort, this is known as runner’s diarrhoea or ‘runners’ trots’. Other common symptoms include abdominal pain and cramping, belching, bloating, nausea, heartburn, flatulence and vomiting. In a study at Maastrict University, The Netherlands, 93% of triathletes had at least one GI symptom, of which 29% were serious enough to affect performance (Jeukendrup et al, 2000).
GI problems are more common in running-type sports possibly due to the physical ‘jostling’ of the intestines during running. All the food inside your GI tract gets shaken and loosened. The reduced blood flow in the intestines and increased levels of stress hormones (due to anxiety before competitions) affect gut motility and this can further exacerbate the condition. And some people’s guts are simply more sensitive than others.
Certain foods may irritate the gut, for example high intakes of fibre, fat, protein or fructose. Dehydration or consuming a drink that is too concentrated in carbohydrate, can also add to the stress on the GI tract
Exercise – specifically more exercise than your body is used to doing – increases intestinal activity.
Solutions
To help alleviate the problem, try doing a short run before the race or doing a warm-up loop around your house before a training run. Alternatively, having a little food before a morning run can help get things moving to enable you to empty your bowels before you head off. Experiment with training at different times of the day.
Reduce your intake of high fibre and gas-producing foods the day before as well as the day of the race. Common culprit foods include bran cereals, cruciferous vegetables (such as cabbage, cauliflower and broccoli), beans, lentils and caffeine. For some people, energy gels and bars can cause problems as can high-fructose foods and drinks. Fructose is absorbed relatively slowly from the gut and, in high concentrations (especially in the form of a drink) can cause GI symptoms.
Start your workout or race fully hydrated. Some athletes avoid drinking in the misguided belief that it causes GI symptoms whereas, in fact, dehydration may be the culprit.
Make your sports drink more dilute. Some people find anything above 5g/ 100g sits in their stomach and causes discomfort.
Train your gut by regularly consuming carbohydrate foods or drinks during training. Start with very small amounts then gradually increase the amount and frequency. It is possible to increase the number of carbohydrate transporters in your gut so that you become better able to digest and absorb carbohydrate during exercise.
Find what works for you. It may take quite a bit of ‘trial and ‘error’ but by practising your race fuelling and hydration strategy during training there will be less risk of problems on race day.
If you enjoyed this post and want to find out more about sports nutrition, then check out the new edition of The Complete Guide to Sports Nutrition , the definitive practical handbook for anyone wanting a performance advantage. It’s the 8th edition (the 1st edition came out in 1993!) and it has been fully updated and revised to bring together the latest research and information on sport and exercise nutrition. It covers topics such as
Maximizing endurance, strength and performance
Carbohydrate, protein and fat requirements
Sports supplements
Improving body composition
Eating plans to cut body fat, gain muscle and prepare for competition
If you enjoyed this post and want to find out more about sports nutrition, then check out my latest book, 