Does Intermittent Fasting Increase or Lower Testosterone?

Intermittent fasting (IF) has exploded in popularity over recent years for its variety of health and body composition benefits. But what does the science say about how reduced eating frequencies and fasting windows impact testosterone production – the crucial hormone that powers male health? In this comprehensive article, we analyze the latest research examining links between popular IF regimes and testosterone levels in men. 

What Is Intermittent Fasting and Why Do People Follow It?

Intermittent fasting simply means going extended time periods consuming zero or markedly reduced calories, alternating with periods of normal eating. Common IF approaches include alternate day fasting, 5:2 plans, and daily 16:8 timed protocols. Reasons people try IF are multifaceted, but chief claims around better body composition, focus and longevity relate to hormonal and biological optimizations from fasting periods. The notion is that temporarily abstaining from food may provide anti-aging and disease-fighting benefits by triggering protective and rejuvenating genes.

Key Intermittent Fasting Facts:

– Alternating extended fasts with normal eating periods 

– 5:2, alternate day and 16:8 regimes are popular

– Proposed benefits include weight control, focus, longevity

– Fasting may trigger beneficial genes reducing aging

How Might Intermittent Fasting Influence Testosterone?

There are clear metabolic links between body fat levels, insulin sensitivity and testosterone production in men. Obese men tend to show lowered testosterone, while weight loss can help rebalance hormones. IF directly assists fat loss and improves insulin function. So in theory, IF could provide knock-on testosterone benefits mediated through enhanced body composition and insulin sensitivity upgrades. However, extreme calorie deficits and overtraining associated with some IF regimes may negatively impact anabolic hormones. Starvation level deficits can backfire, slowing metabolic rate. As men require higher energy intakes for testosterone production, under-eating could suppress testosterone if too aggressive. The question remains whether practical IF plans help or hinder male hormone levels.

Potential Influence Pathways:

Benefits:

– Assists fat loss and insulin function

– Could raise testosterone indirectly

Drawbacks: 

– Very low calorie plans may backfire 

– Under-eating risks slowing metabolic rate

– Could reduce testosterone production   

Weight Loss Fasting Trials Show Testosterone Increases

Initial clinical trials on fasting plans for weight loss provide promising signals for testosterone. Obese men placed on alternate day fasting regimes or 4 weeks of alternate day 650 calorie intakes showed average testosterone increases of up to 180 ng/dL – bringing many men from low baseline levels back up to healthy ranges. However, these studies didn’t isolate IF from weight loss. Participants lost 8-10% body weight – so improvements could simply reflect benefits automatically conferred by shedding excess fat. Lean participants showed no clear testosterone change. So as expected, early data indicates IF assists testosterone only secondary to aiding fat and weight reductions. 

Early Weight Loss Fasting Evidence:

– Obese men showed raised testosterone up to 180 ng/dL

– Benefits linked to 8-10% weight loss

– No benefits for lean men

Pure Time-Restricted Feeding Shows No Effect

To truly isolate IF, longer trials of “early time-restricted feeding” (eTRF) provide insight free of weight loss. Men were assigned normal weight loss diets with exactly equal calories, protein and lifts – the only difference being one group ate earlier, finishing dinner by 2-3pm. Across 8 weeks, eTRF failed to positively or adversely alter testosterone, strength or any hormone biomarker versus normal diet controls eating later. This high quality data demonstrates for weight-stable men, compressed eating itself does not directly influence testosterone or training adaptations. Benefits likely hinge on supporting fat loss indirectly. 

Quality eTRF Evidence:

– Zero calorie difference – only early meal timing 

– 8 weeks showed no impact on testosterone 

– No change in strength or any hormone biomarker  

– Indicates no direct hormonal impact from IF itself

Are More Aggressive Fasting Protocols Risky?

Lastly, an important caution regards taking IF to extremes with multi-day total fasts. Evidence here finds the line between stimulation and suppression may exist with extended fasting. In one troubling case, a man showed severely depleted testosterone levels after 7 days without food – crashing from 650 ng/dL pre-fast down to just 28 ng/dL. Thankfully, his hormone levels rapidly normalized after fasting concluded and calories reintroduced. Still, this demonstrates the potential testosterone suppression risks of very aggressive fasting regimes. Moderate IF likely provides a sweet spot between helpful sustainable calorie deficits and risky hormone downsides of extreme under-eating.

Risks of Prolonged Fasting:

– Total fasting beyond 3-5 days may severely suppress testosterone

– One subject saw test levels crash from 650 ng/dL down to only 28 ng/dL  

– Cautions against overly aggressive fasting regimes

Conclusion

Overall, research suggests intermittent fasting holds modest testosterone benefits for overweight men purely secondary to assisting safe weight reduction of 5-10% body mass. However, for lean men, quality data indicates no direct testosterone or muscle boosting effects from compressed eating alone when calories remain identical. And caution is urged regarding extreme multi-day fasting due to risks of excessive testosterone depletion. In summary, moderate practical IF regimes appear reasonably safe for hormones, but only indirectly benefit testosterone via enhanced weight control. Lean men seeking direct androgen boosting or muscle gain should not view IF as a shortcut past balancing proper nutrition, lifestyle and training fundamentals.