Do Low-Carb Diets Tank Your T?
Some claim that low-carb diets boost testosterone. Others claim the opposite. They’re both right. Here’s what you need to know.
You’ve probably heard that low-carb diets reduce your natural testosterone production. Or maybe you’ve heard that low-carb diets increase testosterone production. So, which is it?
Well, it seems that the two factions of the Carb Cartel – low-carb influencers and higher-carb advocates – have both been cherry-picking studies to support their preconceived notions. The facts, of course, are more nuanced.
What We Know
If we examine dozens of studies (and we did), here’s what we can conclude:
Some very low-carb or keto diets can lower testosterone levels by a little or a lot. This drop is usually temporary, but not always. Low-carb eating can also boost testosterone levels... or maybe it’ll do nothing at all.
“Listen to the science,” they say. But the science is all over the place. So, let’s break it down simply and look at some ways to optimize low-carb diets without risking any hormonal havoc.
What is Low-Carb Exactly?
In the studies we examined, it varies. For a very low-carb (VLC) diet, many studies consider that to be 5% of total calorie intake, which might be around 25 grams daily for a person on a 2000-calorie diet. Other studies define low-carb as 50 grams or below, though a person may need fewer (20-30g) if the goal is ketosis.
How Low Carbs Can Lower T
- Carbohydrates influence insulin levels, which can affect testosterone production. Insulin enhances glucose uptake in cells, including Leydig cells in the testes, where testosterone is synthesized. A VLC diet, by drastically reducing carbs, lowers insulin levels, potentially limiting this support mechanism.
- Research, such as a 2021 study published in Nutrients, found that men on a ketogenic diet (less than 50g carbs/day) for 8 weeks experienced a slight decline in total testosterone compared to a control group on a standard diet. The reduction was attributed to lower insulin and possible stress on metabolic pathways.
- VLC diets can increase cortisol levels due to the body’s adaptation to ketosis, where glycogen depletion triggers a stress response via the HPA axis. Elevated cortisol can suppress T production through negative feedback on the HPG axis. A study in The Journal of Strength and Conditioning Research observed that athletes on VLC diets showed higher cortisol and lower testosterone-to-cortisol ratios, suggesting a catabolic shift.
- Many VLC diet studies involve caloric restriction (most low-carbers are dieting for fat loss, after all), which independently lowers testosterone. A review in Hormones and Behavior noted that energy deficits, regardless of macronutrient composition, reduce luteinizing hormone (LH) pulsatility, impairing testosterone synthesis. If a VLC diet is hypocaloric (low calorie), this could exacerbate testosterone reductions.
- A VLC diet’s effect on testosterone may depend on the dieter. Lifting can mitigate testosterone declines by stimulating the HPG axis. One study showed that keto-adapted athletes maintained testosterone with heavy lifting, unlike sedentary people. (Lesson: If you’re going to do a low-carb diet, lift weights.)
- Initial drops in testosterone on VLC diets may reflect an adaptation phase (2-4 weeks) as the body shifts to fat metabolism. A study in Sports Medicine found that after keto-adaptation (8-12 weeks), T levels often stabilized or returned to baseline in trained individuals, suggesting that acute reductions may not persist.
How Low Carbs Can Boost T
- VLC diets, particularly keto, are typically high in fat. Dietary fats (especially saturated and monounsaturated) are precursors to steroid hormone synthesis, including testosterone. A study in The Journal of Clinical Endocrinology & Metabolism found that higher fat intake correlated with increased T levels in men, suggesting that the high-fat component of VLC diets could offset carbohydrate loss. So, a man who’d been eating a very low-fat diet might see a T boost on a low-carb plan with adequate fats.
- Moderate protein intake in VLC diets (often 15-25% of calories) may support testosterone. If protein remains sufficient, the anabolic environment could be preserved despite low carbs.
Final Answer?
Very low-carb diets can reduce testosterone levels, particularly in the short term, in sedentary individuals, or when paired with caloric deficits due to lower insulin, elevated cortisol, and metabolic stress. However, they don’t universally reduce testosterone. With sufficient fat and protein intake, adaptation over time, and resistance training, T levels may stabilize or even increase.
Ways to Offset a Possible T Drop
If your testosterone takes a hit while on a low-carb plan, the drop is generally mild to moderate, ranging from 5% to 30% below baseline, with most cases falling in the 10-20% range. Much depends on the flavor of the low-carb diet you adopt, but here are some general tips for avoiding this decrease:
1. Spend Your Allotted Carbs Around Workouts
Consume a workout nutrition drink to combat cortisol’s negative effects, trigger the right amount of anabolic insulin at the right time, and boost workout performance (which could otherwise be hampered by dieting). For example, Surge Workout Fuel (Buy at Amazon) contains 34 grams of carbs (mostly from the super-carb HBCD). That fits into most VLC diet allotments; you just have to keep carb intake tight for the rest of the day.
Another option? Eat a pre-workout performance protein bar, like Finibar.
2. Strategically Take a T-Booster
In most studies showing a drop in testosterone, the effect only lasts from 2 to 8 weeks during the initial adaptation phase, which varies among individuals. It might be wise to counter this drop with a natural T booster. Take just one softgel per day of Omega-Man High Absorption Longjack (Buy at Amazon), which contains 300mg of LJ100 per dose, 50% more than standard clinical dosing.
