What really trips up plant-based athletes (and the fix)

Three weeks after going vegan, a client told me his lifts had stalled and he was tired all the time, and he had already decided the diet was the problem. He was not wrong that something had changed. He was wrong about what. He had swapped chicken and eggs for rice and vegetables and quietly dropped from about 1.6 grams of protein per kilo to barely 1. The plant-based diet did not weaken his training. Eating less protein did, and he had blamed the plants.

This is the pattern I see with almost every athlete who trains plant-based and struggles. The problem is rarely the absence of meat. It is two specific, fixable things that hide behind it. Sort those and plant-based fuelling holds up under real training.

TL;DR: Plant-based diets support hard training and muscle growth when two things are handled: enough total protein spread across the day, and iron and B12 checked with a blood test rather than guessed. Head-to-head studies show equal strength and muscle gains when protein is matched, so the meat itself is not what limits performance.

Can you actually build muscle without meat?

Yes, and the head-to-head research is clearer than most people expect. In a 2021 study, 19 vegan and 19 omnivore men followed the same 12-week resistance programme with protein matched at 1.6 grams per kilo, one group using soy and the other whey. Both built the same muscle size and strength (Hevia-Larraín et al., 2021). The protein source did not decide the outcome. The amount did.

That fits the official position. "Appropriately planned vegetarian, including vegan, diets are healthful, nutritionally adequate, and appropriate for all stages of the life cycle, including for athletes," according to the Academy of Nutrition and Dietetics (2016). The phrase carrying all the weight there is "appropriately planned." A plant-based diet does not fail an athlete on its own. A poorly built one does, and so does a poorly built omnivore diet. Your muscles cannot tell whether the leucine arrived in a chicken breast or a bowl of tofu and lentils. They can tell whether there was enough of it.

The first real issue: total protein, spread across the day

Most plant-based athletes who feel weak are simply eating less protein than they think. For building and keeping muscle, 1.4 to 2.0 grams per kilo of body weight per day covers most people who train (ISSN, 2017), and plant eaters sit at the higher end because plant proteins are a little harder for the body to use and lower in leucine, the amino acid that switches on muscle building.

Two things fix this. First, hit the daily total, which for a 70 kilo athlete means roughly 110 to 140 grams, not the 70 or 80 that vegetables and grains drift toward on their own. Second, spread it out: aim for a solid protein source at every meal rather than one big hit at dinner. In practice that looks like tofu, tempeh, seitan, soy milk, lentils, beans, edamame, and a plant protein powder when a day runs short. The honest catch, which the reassuring articles skip, is that reaching 1.6 grams per kilo on whole plants alone takes planning and volume. It is doable. It is not automatic.

The second real issue: iron and B12, checked not guessed

The tiredness that gets blamed on "not eating meat" is often low iron or low B12, and both are common enough on a plant-based diet that you should measure them rather than hope. Up to half of female and endurance athletes run low iron stores, flagged when serum ferritin drops below about 35 micrograms per litre (West et al., 2023). Around 52% of vegans in one large dataset were B12 deficient (West et al., 2023), because reliable B12 comes only from fortified foods or a supplement.

So two rules. B12 is not optional on a vegan diet: take a supplement or eat fortified foods every day, full stop. Iron is different, because more is not automatically better and too much is harmful. If you feel flat, heavy-legged, or breathless on easy runs, get ferritin and B12 tested before you reach for a supplement, and pair plant iron sources like lentils, tofu, and dark greens with vitamin C to absorb more. One reader on a running forum put the frustration well: "Ferritin at 14 would explain a lot, especially with the fatigue and slower recovery." The number explains what willpower cannot.

Building a plant-based training day that holds up

A day that works is less complicated than the worry around it. Anchor every meal with protein: tofu scramble or soy yoghurt and oats at breakfast, lentils or tempeh and grains at lunch, beans or seitan at dinner, with edamame, nuts, or a shake to close any gap. Eat enough total food, because plant diets are filling and it is easy to undereat by accident, which is its own cause of low energy and stalled training.

Take your daily B12, keep an eye on iron with an occasional test, and get enough calcium, iodine, omega-3, and vitamin D from fortified foods or supplements where your diet is thin. None of this asks you to abandon plant-based eating. It asks you to build it on purpose, which is exactly the work I do with vegan and vegetarian athletes rather than telling them to go back to meat.

Frequently asked questions

Can you build muscle on a vegan diet?

Yes. When protein is matched, vegan and omnivore athletes build the same muscle and strength on the same training. The requirement is hitting enough total protein, around 1.6 to 2.0 grams per kilo for those building muscle, and spreading it across meals rather than relying on the plants to add up on their own.

Do vegans need more protein than meat eaters?

Slightly. Plant proteins are a little less usable and lower in leucine, so plant-based athletes are usually advised to aim toward the higher end of the range and to include a range of sources like soy, legumes, and grains across the day. The gap is small and easily covered with planning.

Why am I so tired since going vegan?

Usually one of three things: eating less total protein than before, taking in fewer calories because plant food is filling, or low iron or B12. The first two you fix on the plate. For the third, get ferritin and B12 tested rather than guessing, since iron in particular should not be supplemented blind.

Is plant protein as good as whey for building muscle?

For building muscle over a training block, matched-protein studies show comparable results. Whey is higher in leucine per gram, so plant eaters compensate with slightly more total protein and good sources like soy. Convenience aside, the source is not what decides your progress.

Plant-based training does not cost you performance. Under-eating protein does, and so does ignoring iron and B12 until you feel flat. Get those right and your ethics and your training stop competing. If you want a plant-based plan built around the food you already eat and the way you actually train, book an online consultation and we will build it together. Message Bela on WhatsApp to book a plant-based sports nutrition consultation.

This article is educational and is not a substitute for individual medical or nutritional advice.