Keto and Testosterone: What the Research Actually Shows

The ketogenic diet has been popular for over a decade, promoted for fat loss, mental clarity and metabolic health. It typically restricts carbohydrates to a small amount per day so that the body produces ketones for fuel. For men interested in hormonal health, the obvious question is whether keto helps or hurts testosterone.

Online, you will find confident claims in both directions. The research is more nuanced, and it does not support the idea that keto reliably lowers testosterone, or that it reliably raises it. This article walks through what the main reviews and trials actually found.

What the Meta-Analyses Say

Two systematic reviews with meta-analysis cover this topic, and they reach different headlines.

Ketogenic diets and testosterone. Pooling 7 studies (8 trials, 230 participants), the authors reported a significant increase in total testosterone after ketogenic diets, larger with very low calorie ketogenic diets than with normal-calorie keto. The rise was correlated with weight loss and age. Only three of the studies enrolled overweight or obese men, and the authors noted that the included studies lacked information about the hypothalamic-pituitary-gonadal hormones needed to explain the mechanism.^[1] In plain terms: when keto leads to weight loss, testosterone tends to improve, as it does with weight loss in general.^[4]

Low-carb diets, cortisol and testosterone. A meta-analysis of 27 intervention studies with 309 healthy men defined low-carb as 35% of energy or less from carbohydrate. In diets lasting under 3 weeks, low-carb eating moderately increased resting cortisol, whereas longer diets had no consistent effect on resting cortisol. After long-duration exercise (20 minutes or more), cortisol was much higher on low-carb than high-carb diets. For testosterone, moderate-protein low-carb diets had no consistent effect on resting total testosterone, while high-protein (35% or more) low-carb diets greatly decreased resting total testosterone (about 5.2 nmol/L).^[2]

The takeaway from that review is less about carbohydrates and more about protein share: very high protein intakes appear to be where testosterone dropped. That is a reason not to build a low-carb diet on an extreme share of protein. See our guide to protein and testosterone.

Cortisol: A Short-Term Stressor, Not a Permanent One

Cortisol is your main stress hormone, and chronically high cortisol can work against testosterone, as covered in our article on stress, cortisol, and testosterone. Online claims often say keto keeps cortisol permanently elevated. The meta-analysis above found something more modest: cortisol rose during the first three weeks and then appeared to return to baseline at rest, although it stayed higher after long exercise sessions.^[2] That could matter to people doing long, hard endurance sessions on very low carbohydrate intake, but it has not been shown to lower testosterone in these studies.

Trials in Trained Men

Fears that keto would hurt athletes are not supported by the small trials we could find:

• In 25 resistance-trained college-aged men, a 10-week ketogenic diet alongside a lifting program was compared with a Western diet. Total testosterone increased by 118 ng/dL in the keto group versus a decrease of 36 ng/dL in the Western diet group, measured at weeks 0 and 11 (after carbohydrates were reintroduced in week 11). Strength and power improved similarly in both groups.^[5]
• In 20 experienced, resistance-trained middle-aged men eating a calorie-reduced diet for 8 weeks, ketogenic and non-ketogenic low-carb groups had similar changes: basal testosterone and free testosterone increased in both, and strength and body composition changes were similar.^[6]

These are small studies with short durations, so they cannot rule out problems in other people or over the long term. They do not support the claim that keto reliably crushes testosterone in active men.

A Signal Worth Watching: Free Testosterone and SHBG

A Danish randomized crossover trial of middle-aged adults with obesity compared three weeks of a ketogenic diet with a standard diet. Total testosterone in men was not significantly different (p = 0.1), but SHBG rose and free testosterone fell on keto, as did free estradiol. The authors state that the clinical impact of the reduction remains to be investigated.^[3] The study was small (11 adults, men and women analyzed separately) and short, so it is a signal rather than a conclusion. For background on why SHBG matters, see our article on free vs. total testosterone.

What About Thyroid Hormones?

Thyroid hormone is part of the broader hormonal picture. Older research in people with obesity on very low-calorie diets found that serum T3 (the active thyroid hormone) fell and reverse T3 rose on ketogenic diets, and the T3 change correlated with ketone levels, whereas a low-calorie non-ketogenic diet produced only a transient change.^[7] That study involved severe calorie restriction, so it does not show what a normal-calorie keto diet does in healthy men. If you notice persistent fatigue, feeling cold or hair thinning on a very low-carb diet, speak to a doctor.

Who Should Be Cautious

Keto is not a neutral choice for everyone. It can cause side effects during the first weeks, can interact with some medications such as diabetes drugs, and is unsuitable for some medical conditions.^[8] Talk to a doctor or dietitian before starting if you:

What Actually Moves Testosterone

The consistent pattern across these studies is that weight change and overall health matter more than any single macronutrient. If you are carrying excess body fat, losing weight by any sustainable method tends to raise testosterone, and a diet you can stick to is more useful than a perfect one you abandon. If you are already lean and healthy, there is no good evidence that either keto or high-carb eating is better for testosterone, and the basics apply: enough calories, adequate protein, good sleep, resistance training and stress management.

The Bottom Line

The research does not support the claim that keto lowers testosterone, and it does not support the claim that keto boosts it. In people with excess weight, weight loss from keto is associated with higher testosterone. In trained men, small trials show stable or higher testosterone. Very high protein intakes within low-carb diets, short-term cortisol changes and a drop in free testosterone in one small trial are the signals to watch. Choose the dietary pattern you can sustain safely and focus on the fundamentals.

For a deeper look at how food choices affect your testosterone, explore our guides on testosterone-boosting foods, and on the opposite end of the spectrum, whether a carnivore diet supports testosterone.