Dietary fat and hormones

What the research actually found

The claim that low-fat diets reduce testosterone has been circulating for years, usually without the numbers. Here they are.

A 2021 systematic review and meta-analysis of six controlled intervention studies (206 participants) found that when men switched from a high-fat diet (around 40% of calories) to a low-fat diet (around 20%), testosterone decreased by 10–15% on average. Vegetarian low-fat diets showed larger reductions, up to 26%.

The honest complication: a more recent meta-analysis on the same question reached a different conclusion, finding no clear effect. This is a genuinely unsettled literature with a small number of small studies, and anyone presenting either result as definitive is overstating it.

Which means the sensible reading is: there may be a modest effect at the low end, so do not eat a very low-fat diet. That is a cheap precaution against an uncertain risk, and there is no reason to go further than it.

Putting the size of the effect in perspective

A 10–15% change in testosterone sounds substantial. Some context is needed to use it properly.

• Normal reference ranges are wide. A 10–15% move within the normal range has no established effect on muscle growth in men who are not clinically deficient.
• Natural variation is larger. Testosterone varies with time of day, sleep, illness and stress by amounts comparable to this.
• Sleep restriction has a bigger effect. A week of five-hour nights reduces testosterone by more than this dietary change does — see sleep and strength.
• Body fat and total calories matter more. Being substantially overweight, or in an aggressive prolonged deficit, affects hormones more than fat percentage does.

Setting your fat intake

The practical order of operations for building a diet:

1. Protein first. 1.6–2.2 g/kg — see how much protein you actually need.
2. Fat to a floor. At least 0.5 g/kg, ideally 0.7–1.0 g/kg, or 20–35% of calories.
3. Carbohydrate fills the rest. The most flexible of the three — see carbohydrates around training.

For an 80 kg person eating 2,600 kcal, that is roughly 160 g protein, 60–80 g fat and 320–370 g carbohydrate. In a deficit at 2,100 kcal, fat is where you should be least aggressive — take the reduction mostly from carbohydrate, keeping fat near the floor rather than below it.

Fat quality, which matters for different reasons

The hormonal question is about total fat. Fat type matters for cardiovascular health, which is a longer-horizon concern and arguably the more important one.

• Monounsaturated fats — olive oil, avocado, nuts. Make these the bulk of your intake.
• Omega-3 fats — oily fish twice a week, or a supplement if you do not eat fish. The best-supported case for a fat-related supplement.
• Saturated fat — from meat, dairy, coconut oil. Not to be eliminated; current guidance is to keep it under about 10% of calories.
• Industrial trans fats — banned or heavily restricted in most markets now. Avoid entirely where they remain.

Some older studies associated saturated fat intake specifically with testosterone. The evidence is weak, and it is not a good reason to eat a lot of it.

Women and dietary fat

Most of the testosterone literature is on men, which leaves an important gap. What is reasonably established for women:

• Very low fat combined with low total calories is the real risk, and it presents as menstrual disruption rather than as a testosterone number.
• Menstrual irregularity is a signal to take seriously. It usually indicates low energy availability rather than low fat specifically — the fix is more total food.
• Fat-soluble vitamin absorption (A, D, E, K) requires dietary fat, and this applies to everyone.
• The same floor applies: at least 0.5 g/kg, and higher if calories allow.

If your cycle changes during a diet, that is a reason to raise calories, not to push harder. See building a calorie deficit you can sustain.

Common questions

Will eating more fat raise my testosterone?

Only if you were eating very little. Beyond about 30% of calories there is no evidence of further benefit.

Is a keto diet good for hormones?

It is high-fat, so it will not be low-fat, but there is no established hormonal advantage. It does cost carbohydrate for high-volume training — see carbohydrates around training.

Do I need a testosterone-boosting supplement?

No. Almost nothing in that category has good evidence in men who are not deficient, and the few things that matter — sleep, body fat, adequate calories — are free.

How low is too low?

Below 0.5 g/kg, or below about 15% of calories, is where problems start appearing.

Should I cut fat or carbs to lose weight?

Whichever you find easier to sustain, keeping fat above the floor. Total calories determine the result.

Does cholesterol in food matter for testosterone?

Dietary cholesterol has little effect on either blood cholesterol or hormones for most people. Eggs are fine.

The practical version

• Keep fat at 20–35% of calories, or at least 0.5 g/kg — ideally 0.7–1.0 g/kg.
• One meta-analysis found 10–15% lower testosterone at 20% fat versus 40%; a newer one disputes it.
• The effect, if real, is smaller than that of poor sleep or excess body fat.
• Set protein first, fat to a floor, carbohydrate with the remainder.
• In a deficit, cut carbohydrate before fat once fat is near the floor.
• For women, very low fat plus low calories shows up as menstrual disruption — raise calories.