The Best Diet for Testosterone: Low-Fat, Keto, Vegan and Fasting Compared

Two men, same age, same gym. One went keto in January and swears his testosterone has never been higher. The other cut out meat and most fat after a bad cholesterol result, lost six kilos, and now feels flat in a way he cannot quite describe.

Both of them are partly right, and both of them are missing the bigger point.

Diet does affect testosterone. But the differences between the popular diets are smaller than the internet suggests, and they are dwarfed by one variable most arguments ignore: how much body fat you are carrying, and whether the diet you choose makes it go down.

The one number that matters more than the diet

In 2013, Corona and colleagues pooled the studies of weight loss in men with obesity and low testosterone. A low-calorie diet raised total testosterone by an average of 2.87 nmol/L. Bariatric surgery, which produces much larger weight loss, raised it by 8.73 nmol/L.

The best predictor of how much testosterone rose was not which diet was used. It was how much weight was lost.

Keep that in mind through everything below. If you are overweight, the best diet for your testosterone is the one you can stick to long enough to lose fat, and the macronutrient split is a secondary question. If you are already lean, the picture changes, and some approaches carry a real cost.

Why fat matters so much is explained in stubborn belly fat in men and fatty liver and testosterone: fat tissue converts testosterone into oestrogen, and the insulin resistance that travels with it suppresses the hormone that carries testosterone in the blood.

Low-fat diets

This is the approach with the clearest downside.

A 2021 systematic review and meta-analysis by Whittaker and Wu looked at controlled studies that moved men from a higher-fat to a lower-fat diet. Across six studies and 206 men, low-fat diets reduced total testosterone, free testosterone and dihydrotestosterone. The largest drops were in the two studies that used vegetarian low-fat diets.

The effect is modest in size, and the authors call for larger trials. But the direction was consistent.

Population data points the same way. In 2020, Fantus and colleagues analysed more than 3,100 American men from the NHANES survey. The average testosterone across all men was 435.5 ng/dL, roughly 15.1 nmol/L. Men following a low-fat diet averaged 411 ng/dL, about 14.3 nmol/L, and the association held after adjusting for age, weight, activity and health conditions.

The surprise in that paper was that men following a Mediterranean-style diet also averaged slightly lower, at 413 ng/dL. The authors were careful to say the clinical significance of such small differences is unclear, and diet was assessed by questionnaire. It is not a reason to abandon a Mediterranean diet, which has strong evidence for heart health. It is a reason to be sceptical of anyone who claims one diet reliably lifts testosterone.

What this means in practice

If you have moved to a very low-fat diet for cholesterol, your doctor's advice still stands. But very low fat is not the only way to improve cholesterol, and there is no reason to fear foods like extra virgin olive oil, eggs, nuts and oily fish. Replacing saturated fat with unsaturated fat is a different thing from cutting fat to the bone.

Keto

Keto has the most enthusiastic testosterone claims, and one study behind many of them.

In a trial published in the Journal of Strength and Conditioning Research, Wilson and colleagues put 25 college-aged men on a resistance training programme for 11 weeks, with either a ketogenic diet or a conventional Western diet. Total testosterone rose by 118 ng/dL on keto and fell by 36 ng/dL on the Western diet. Strength and power improved equally.

The detail usually left out is lean mass. During the ten weeks of keto, the keto group gained 2.4 per cent lean mass against 4.4 per cent in the Western diet group. The keto group only caught up after carbohydrates were reintroduced in week 11, which may partly reflect water and glycogen returning to the muscle rather than new tissue.

So keto did not stop these men getting stronger, and it helped them lose slightly more fat, 2.2 kg against 1.5 kg. But it is one small, short trial in young trained men, and it is not proof that keto raises testosterone in anyone else.

The trade-offs

Hard training on very low carbohydrate is uncomfortable for many people, especially for high-rep work and conditioning. Keto also raises LDL cholesterol noticeably in some people, so if you try it for more than a few weeks, get your lipids checked. And like any diet that works for fat loss, most of its testosterone benefit in overweight men probably comes from the fat loss itself.

Vegan and vegetarian

The idea that plant-based eating destroys testosterone is mostly a myth, with one real caveat.

The best-known study, by Allen and colleagues in 2000, compared 233 vegan men with 226 meat-eaters and 237 vegetarians in Britain. Vegans actually had higher total testosterone. They also had higher SHBG, the protein that binds testosterone in the blood, so their free testosterone was no different from the other groups.

If SHBG and free testosterone are new terms, those two guides explain why the difference matters.

Soy is the usual worry, and it is largely misplaced at normal food intakes. We cover the evidence in does soy lower testosterone.

The real caveat is the one from the low-fat section. A vegan diet that is also very low in fat is the combination that showed the biggest drops in controlled studies. Nuts, seeds, avocado and olive oil make a real difference here.

Nutrients to watch

Plant-based diets can run short of vitamin B12, which needs supplementing, and sometimes zinc and vitamin D. Zinc is harder to absorb from plant sources, so seeds and legumes do more of the work: pumpkin seeds, lentils and chickpeas are useful. More in our guides to vitamin B12 and zinc.

Intermittent fasting

Fasting produces a result that surprises people: it tends to lower testosterone in lean men, and it does not seem to matter much.

A 2016 trial by Moro and colleagues put 34 resistance-trained men on either a normal eating pattern or 16/8 time-restricted eating, with all food eaten within an eight-hour window, for eight weeks. The time-restricted group lost fat mass and kept their muscle and strength, but their testosterone fell.

A 2022 review of human fasting trials by Cienfuegos and colleagues reached the same conclusion across studies: intermittent fasting reduced testosterone in lean, physically active young men, without harming muscle mass or strength. Notably, at the time of that review there were no fasting studies measuring testosterone in men with obesity, which is the group most likely to benefit.

That fits the wider pattern. For a lean man, fasting is another form of energy restriction, and energy restriction nudges testosterone down. For a man carrying excess weight, any method that produces sustained fat loss is likely to help, and fasting is simply one tool for eating less.

Very aggressive dieting

The one approach with a consistently large negative effect is not a named diet at all. It is eating far too little for too long.

Contest preparation for bodybuilding, prolonged military training and extreme calorie cutting all push testosterone down, sometimes into the range seen in clinical deficiency. It usually recovers once food intake returns to normal. If you are already lean and chasing the last few kilos, this is where your testosterone is most at risk, and where our guide to how much muscle you can build naturally is a useful reality check.

What about ultra-processed food?

This is where the diet argument usually misses its target. Whether you eat keto, vegan or something in between, the evidence against a diet built on ultra-processed food is getting stronger. A recent controlled feeding trial found that, at matched calories, men gained more fat on an ultra-processed diet. We cover that study in foods crushing your testosterone.

Any of the diets above, done with whole foods, beats any of them done with packets.

So which diet is best?

There is no single winner, but there is a clear set of rules that hold across all of them.

If you are overweight

Pick whichever approach lets you lose fat steadily and keep it off. Keto, Mediterranean, high-protein, time-restricted eating: the evidence says weight loss drives the testosterone gain, not the label. Avoid going very low in fat.

If you are lean

Eat enough. Avoid long stretches of heavy restriction, very low fat intakes and extended fasting if testosterone is a priority. Keep protein adequate and include fats from fish, eggs, olive oil, nuts and seeds.

Whatever you eat

Build meals around real food. Include zinc-rich foods such as oysters, beef and seeds, oily fish such as salmon or mackerel a couple of times a week, and plenty of vegetables. Keep alcohol moderate, because heavy drinking undoes much of the good, as explained in the truth about alcohol and testosterone. If you want meals that already follow these rules, our recipe collection is a practical starting point.

And measure rather than guess. A testosterone test before a diet change and another three months later tells you more than any argument online.

Common questions

Does keto raise testosterone?

In one small trial in young trained men, testosterone rose on keto compared with a Western diet. That is not strong enough to say it works for everyone, and in overweight men most of the benefit probably comes from fat loss.

Do vegans have lower testosterone?

In the largest comparison, vegan men had higher total testosterone than meat-eaters, balanced by higher SHBG, so their free testosterone was similar. The risk is a vegan diet that is also very low in fat.

Does intermittent fasting lower testosterone?

In lean, active young men it tends to lower testosterone slightly, without harming muscle or strength. There is little direct data in men with obesity, where fat loss would be expected to help.

Is a low-fat diet bad for testosterone?

Controlled studies show low-fat diets reduce testosterone modestly, with the biggest drops on vegetarian low-fat diets. Moderate amounts of unsaturated fat are a safer choice.

What is the single best dietary change for testosterone?

If you carry excess weight, losing fat. The size of the weight loss predicts the rise in testosterone better than the type of diet used to achieve it.

Sources: Corona G et al., Body weight loss reverts obesity-associated hypogonadotropic hypogonadism: a systematic review and meta-analysis, Eur J Endocrinol 2013;168(6):829-43 · Whittaker J, Wu K, Low-fat diets and testosterone in men: systematic review and meta-analysis of intervention studies, J Steroid Biochem Mol Biol 2021;210:105878 · Fantus RJ et al., The association between popular diets and serum testosterone among men in the United States, J Urol 2020;203(2):398-404 · Wilson JM et al., Effects of ketogenic dieting on body composition, strength, power, and hormonal profiles in resistance training men, J Strength Cond Res 2020;34(12):3463-74 · Allen NE et al., Hormones and diet: low insulin-like growth factor-I but normal bioavailable androgens in vegan men, Br J Cancer 2000;83(1):95-7 · Moro T et al., Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males, J Transl Med 2016;14:290 · Cienfuegos S et al., Effect of intermittent fasting on reproductive hormone levels in females and males: a review of human trials, Nutrients 2022;14(11):2343 · Educational only, not medical advice.

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