Training on plants without under-fuelling

Athletes who move to plant-based eating usually arrive worried about protein. Protein is rarely the problem.

The problem is total energy, and it is common enough that I raise it first with almost everyone.

Why it happens

Plant foods are generally less energy dense than animal foods. The same volume of food contains fewer calories.

An athlete who was eating enough on a mixed diet, and who substitutes plant foods without increasing volume or density, ends up in a deficit without changing anything about how much they think they are eating.

Add high fibre content, which increases fullness, and appetite suppression from hard training, and the deficit compounds.

The effect is gradual. People report feeling fine for weeks, then flat.

What under-fuelling does

The syndrome is well described in sports medicine as relative energy deficiency in sport, and it affects far more than performance.

Performance: reduced endurance and strength, impaired recovery, and training that stops producing improvement.

Hormonal: menstrual disturbance in women, up to and including cessation; reduced testosterone in men; thyroid changes.

Bone: reduced bone density and increased stress fracture risk. This is the consequence that is hardest to reverse.

Immune: more frequent illness.

Psychological: low mood, irritability, and a preoccupation with food that people frequently mistake for a discipline problem.

Crucially, this can occur at a stable body weight. The body downregulates other functions rather than losing mass, so the scale does not warn you.

The signs to look for

Performance plateauing or declining despite training. Persistent fatigue. Feeling cold constantly. Recovery taking longer than it used to. Frequent minor illness. In women, changes to or loss of menstrual function. Reduced libido. Poor sleep. Low mood.

Loss of menstrual function is never normal in an athlete and always warrants medical assessment.

Increasing energy density

The practical fix. You need the same energy in less volume.

Add fat deliberately. Olive oil on everything. Tahini in dressings and sauces. Nut butters. Avocado. Coconut milk in curries and porridge.

Fat provides more than twice the energy per gram of carbohydrate or protein, and it is the most efficient lever available.

Use less bulky forms of the same foods. Fruit juice and dried fruit alongside whole fruit. Smoothies rather than salads. Nut butter rather than whole nuts.

Reduce fibre around training, which is standard sports nutrition advice and matters more here because baseline fibre intake is higher.

White rice, white bread, peeled potatoes and refined pasta around sessions are appropriate. Wholegrain everything, all the time, is not the goal for an athlete.

Drink calories. Smoothies with soy milk, nut butter, banana, oats and dates. Recovery drinks. This is the fastest way to add substantial energy when appetite is limited.

Eat more often. Five or six eating occasions rather than three, since volume per sitting is the constraint.

Carbohydrate around training

Plant-based diets tend to be higher in carbohydrate, which suits endurance training well. The issue is timing and form.

Before training: lower fibre, lower fat, easily digested. Toast with jam, a banana, white rice, a sports drink.

A high-fibre meal before a hard session is a common cause of gastrointestinal trouble.

During, for sessions over roughly an hour: standard carbohydrate intake recommendations apply and most sports products are already plant-based.

After: carbohydrate and protein together. Soy milk with a banana and some oats does the job.

Protein for athletes

Higher than the general recommendation, in the range of 1.4 to 2.0 grams per kilogram, and toward the higher end for those eating exclusively plant protein.

Practically: a protein source at every meal, larger portions than feel necessary, and soy foods used deliberately since they are the densest option.

Protein powder is useful here, not because plant protein is inadequate, but because hitting a high target on plant food alone requires eating a great deal.

Distribution across four or five feedings appears slightly better than concentrating it, and there is some evidence supporting a dose before sleep.

The nutrients to actively manage

Beyond energy, several matter more for athletes.

Iron. Requirements are higher in athletes, particularly endurance athletes and menstruating women, and plant iron is less well absorbed. Test rather than guess, and do not supplement without testing.

B12, non-negotiable, covered elsewhere on this site.

Vitamin D, which affects muscle function and bone.

Calcium, for bone health, particularly relevant given the stress fracture risk if energy availability is low.

Omega-3, where an algal supplement is the practical route to the long-chain forms.

Creatine, which is found almost exclusively in animal foods. Vegetarians and vegans have lower muscle stores and tend to show larger responses to supplementation. Among the best-evidenced supplements available, and a reasonable one for plant-based athletes doing high-intensity work.

Iodine and zinc, both worth attention.

The thing to check first

Before adjusting anything else: track intake honestly for a few days, including weekends.

Most athletes I work with who feel flat are eating several hundred calories a day less than they think, and fixing that resolves most of the symptoms attributed to the diet itself.

General information rather than individual advice. Athletes with symptoms of low energy availability, menstrual disturbance, or suspected deficiency should consult a sports dietitian and their doctor. Do not supplement iron without testing.