This Mendelian randomization study investigated genetically predicted fat mass and testosterone in 83,002 men of European ancestry. "These results showed that genetically higher fat mass was associated with lower testosterone levels in men of European ancestry but that genetically predicted fat-free mass was either only weakly associated or not statistically associated with testosterone levels… This MR study suggests that fat mass lowers testosterone levels, while muscle mass may not be related to testosterone levels. Therefore, reducing fat mass may be necessary to maintain or elevate testosterone levels."

This systematic review and meta-analysis assessed the relationship between low-fat diets and testosterone levels in men through intervention studies. "There were significant decreases in sex hormones on low-fat vs high-fat diets… total testosterone [-0.38…], free testosterone [-0.37…], urinary testosterone [-0.38…], and dihydrotestosterone [-0.3…]." The authors note: "Low-fat diets appear to decrease testosterone levels in men, but further randomized controlled trials are needed to confirm this effect." Luteinizing hormone and sex hormone–binding globulin showed no significant changes, suggesting the effect was primarily on androgen levels.

A Reuters report says that being overweight or obese is strongly associated with lower testosterone levels, while also noting that lifestyle factors can affect male hormone decline. This supports the broader relationship between body fat status and testosterone, but it does not specifically claim that very low body fat lowers testosterone.

In a cross-sectional study of 1225 male participants, percent body fat was analyzed in relation to sex hormones. "Percent body fat was negatively correlated with testosterone levels and positively correlated with estradiol levels (both P < 0.05)… In conclusion, our results showed that lower testosterone levels in males are linked to more total fat percent and less lean mass percent."

This review from the Endocrine Society journal emphasizes obesity as the main clinical correlate of lowered testosterone. "Serum testosterone concentration is often reduced in men with obesity, proportional to the degree of excess weight… However, obesity is not a cause of pathological hypogonadism… There is no high-quality evidence supporting obesity as a cause of pathological hypogonadism." The authors frame this as "pseudo-hypogonadism of obesity" that improves with weight loss. No discussion is provided of low body-fat states causing reduced testosterone; the focus is consistently on excess adiposity.

In males, testosterone levels showed a significant negative correlation with total percent fat (TPF) (β = −11.97, P < 0.0001), abdominal percent fat (APF) (β = −9.36, P < 0.0001), gynoid percent fat (GPF) (β = −10.29, P < 0.0001), and the android-to-gynoid ratio (A/G) (β = −320.93, P < 0.0001). Specifically, testosterone decreased by 11.97 ng/dL with every 1% increase in TPF, by 9.36 ng/dL with every 1% increase in APF, and by 10.29 ng/dL with every 1% increase in GPF. In conclusion, our results showed that lower testosterone levels in males are linked to more total fat percent and less lean mass percent.

This narrative review describes mechanisms by which obesity leads to hypogonadism. "Obesity plays a major role in hypogonadism through complex interactions between gonadal hormones, excess adipose tissue aromatase activity and adipocyte hormone production, and inflammatory markers, all of which ultimately results in decreased testosterone production." It notes that "Weight loss is associated with increased free and total testosterone levels in males with hypogonadism." The article focuses on excess fat and does not identify low body fat as a risk factor for androgen deficiency.

This mechanistic review addresses testosterone and adiposity. "Obesity-associated hypotestosteronemia is a functional, non-permanent state, which can be reversible, but this requires substantial weight loss… On the one hand, increasing body fat suppresses the HPT axis by multiple mechanisms via increased secretion of pro-inflammatory cytokines, insulin resistance and diabetes; while on the other hand low testosterone promotes further accumulation of total and visceral fat mass." The paper repeatedly describes a bidirectional inverse relationship between *increased* fat mass and testosterone, and does not report a causal role for very low body fat in suppressing testosterone.

This clinical review from NIH details male obesity-related secondary hypogonadism. "The single most significant risk factor for testosterone deficiency in men is obesity… There is a bidirectional relationship between obesity and hypogonadism. In population-based studies, obesity is the single most important factor resulting in testosterone deficiency… Similarly, testosterone deficiency can cause increased adipogenesis and visceral obesity." The review frames excess body fat as the key factor associated with androgen deficiency and does not mention low body fat as a cause of reduced androgens.

This longitudinal study investigated sex-differential testosterone response to long-term weight loss in adults with severe obesity. "In men, excess body fat is associated with lower testosterone levels due to the conversion of testosterone into oestrogen in fat tissue." The study found: "There was an inverse association between lost weight and serum testosterone level. For each 1 kg weight reduction male subjects' testosterone level increased by 0.6%… the calculated free testosterone increased by 0.5%." The authors report that sustained weight loss was "inversely associated with increase in total testosterone and CFT in males," supporting that reducing excess fat mass raises rather than lowers androgen levels.

This cross-sectional study of adult males analysed body composition and testosterone. It reports that percent body fat was negatively correlated with testosterone: "The findings of this study support a negative association between body fat and testosterone levels in males." In the conclusion the authors state: "Our results showed that lower testosterone levels in males are linked to more total fat percent and less lean mass percent," i.e., higher body fat is associated with lower androgen levels, not vice versa.

The article says that in men with obesity, fat tissue converts testosterone to estrogen, causing testosterone to decrease faster. It also describes a vicious cycle in which lower testosterone promotes further fat accumulation.

This review on secondary male hypogonadism highlights the "hypogonadism-obesity cycle". "Obesity, in turn, may have a direct impact on testosterone levels, contributing to reduced testosterone and increased adipose tissue, creating a negative cycle called the hypogonadism-obesity cycle… In summary, the current evidence is consistent with a bidirectional relationship between visceral fat and testosterone levels, creating a self-perpetuated cycle that promotes insulin resistance." The discussion centers on *excess* visceral and central fat, and does not provide evidence that low or minimal body fat suppresses androgen levels.

This NIH-reviewed article synthesizes evidence on weight loss and testosterone in men. It concludes: "Weight loss (WL), particularly through fat reduction, has a positive influence on testosterone levels. Both moderate and significant reductions in BMI are associated with notable increases in serum testosterone levels." Dietary interventions are described: "Dietary interventions, particularly low-carbohydrate and Mediterranean diets, have been linked to increased testosterone production in men with obesity," indicating that reducing excess fat rather than having low fat per se improves androgens.

This systematic review and meta-analysis of intervention studies found that low-fat (LF) diets led to small to moderate reductions in total testosterone (TT), free testosterone (FT), urinary testosterone (UT), and dihydrotestosterone (DHT) in men. The principal findings indicate that LF diets moderately lower testosterone levels in men, likely by diminishing testicular testosterone production. However, the authors emphasize that further randomized controlled trials are required to confirm this effect.

After diet modulation from a high-fat (>30% calories as fat and low-fiber <20 g/d) to a low-fat diet (about 15% calories as fat and 25–30 g/d of fiber), mean serum testosterone (T) concentration fell (P < 0.0001), accompanied by small but significant decreases in serum free T (P = 0.0045), 5α-dihydrotestosterone (P = 0.0053), and adrenal androgens. We conclude that reduction in dietary fat intake (and increase in fiber) results in a 12% consistent lowering of circulating androgen levels without changing the clearance. Our data indicate that lowering diet fat without reducing weight causes a reduction in serum T, free T, DHT and adrenal androgens in men.

The article reports that a low-fat diet was associated with lower serum testosterone in men. It gives an average serum testosterone of 411 ng/dL for men on a low-fat diet versus 435.5 ng/dL overall, and notes that low-fat dieters had lower testosterone even after adjusting for age, BMI, and activity level.

This review article examines the association between obesity and male hypogonadism. "Obesity is linked to impaired male gonadal function and is currently a major cause of hypogonadism… Thus, compelling evidence highlights a vicious cycle where male hypogonadism can lead to increased adiposity, while obesity can be a cause for male hypogonadism." The authors’ synthesis focuses on overweight/obese states as drivers of lower testosterone and hypogonadism rather than low body fat states.

In a subgroup of 57 men aged 70–80 years, testosterone levels correlated negatively with percentage body fat (r = −0.57), abdominal fat (r = −0.56) and plasma insulin levels (r = −0.40). Moreover, increase in fat mass (obesity), as occurs in aging males, is in itself associated with low levels of free testosterone and GH which both normalize after weight reduction.

This article reports that a Worcester University research team found low-fat diets reduced testosterone in 206 men by about 10% to 15%, and by as much as 26% in men following a low-fat vegetarian diet.

This news report summarizes the University of Worcester systematic review on diet and testosterone in men. It states: "A new study… has found low fat diets decrease men’s testosterone levels by 10–15%." The meta-analysis "combined together the results of 6 well-controlled studies… These studies first put men on a high fat diet (40% fat), and then transferred them to a low fat diet (20% fat), and found their testosterone levels decreased by 10–15% on average. Particularly bad were vegetarian low fat diets causing decreases in testosterone up to 26%." The piece attributes the findings to Whittaker & Wu 2021, indicating that dietary fat restriction can lower androgen levels independent of obesity.

The results of these cross-sectional analyses suggest that higher levels of estradiol (E2) and the ratio of E2 to testosterone (E2/T) in men are associated with greater fat mass, whereas higher levels of testosterone and to some extent sex hormone-binding globulin (SHBG) are associated with lower fat mass. Overall, greater body fat was associated with lower testosterone levels and higher estrogen levels in men.

The article states that the higher the body fat and abdominal fat ratio, the lower the testosterone level tends to be, and that reducing fat is an important factor for raising male hormone levels.

This analysis in *The Journal of Urology* reported on dietary patterns and serum testosterone in US men. According to the summary: "We found that men who adhered to a fat restrictive diet had lower serum testosterone than men on a nonrestrictive diet." Serum testosterone "was lower in men on the two restrictive diets: average 411 ng/dL for those on a low-fat diet and 413 ng/dL for those on the Mediterranean diet" compared with men on an unrestricted diet. The authors note that this provides evidence that a low-fat diet is associated with lower testosterone levels.

This clinical review addresses functional hypogonadism related to obesity. "The hormonal consequences of excess body fat in men are functional hypogonadism, which not only causes clinical symptoms of testosterone deficiency, but is also a risk factor for obesity (a vicious circle mechanism)… Reducing the mass of adipose tissue causes an increase in testosterone concentrations and has a beneficial effect on semen parameters." The article characterizes hyperestrogenism due to obesity and decreased free testosterone, but does not describe low body fat or leanness as a mechanism of androgen deficiency.

The article says that body fat percentage below about 10% was associated with a sharp drop in testosterone, and that reducing calorie intake by more than 30% can also cause testosterone concentrations to fall sharply.

This article from a specialist obesity clinic explains mechanisms of obesity-induced hypogonadism. "Obesity-associated hypogonadism is a hormonal condition seen in some men with excess body fat… Excess fat tissue contributes through hormonal conversion, inflammatory signalling, and metabolic disruption, leading to lower testosterone, impaired fertility, and adverse effects on body composition and energy levels… In men with excess body fat, increased aromatase activity converts more testosterone into oestrogen… As fat mass rises, testosterone levels fall, and oestrogen levels increase." The content consistently links *high* fat mass with lower testosterone and does not claim that low fat mass causes androgen suppression.

This Harvard Health article reviews evidence linking obesity and testosterone. It notes: "Obesity lowers testosterone levels. For example, a 2007 study of 1,667 men ages 40 and above found that each one-point increase in BMI was associated with a 2% decrease in testosterone." A 2008 study found that waist circumference was "an even stronger predictor of low testosterone levels than BMI," with a four-inch increase in waist size increasing the odds of low testosterone by 75%. The article concludes that waist circumference was "the strongest single predictor of developing symptoms of testosterone deficiency," indicating that higher, not lower, body fat is typically associated with reduced androgen levels in men.

This investigation reveals a positive correlation between testosterone levels in the upper quartiles of the normal range and lean mass. Additionally, it indicates a negative relationship between testosterone levels in these quartiles and fat mass in both upper and lower extremities. Thus, within physiological ranges, higher testosterone is associated with lower fat mass and greater lean mass.

This study examined adipose tissue enzyme activity in men with chronic testosterone deficiency. The authors write: "In summary, our data suggest that chronic testosterone deficiency in men alters the adipocyte enzymes involved in fatty acid storage." They report that "Testosterone deficiency in men increases femoral ACS activity, which is associated with the rate of FFA storage in the femoral depot." This indicates that low testosterone can promote changes in fat storage and distribution, suggesting a direction of causality from androgen deficiency to altered adiposity rather than low fat causing low androgen levels.

The post states that very low body fat percentage, especially below 5%, is perceived by the body as an energy-deficit crisis and commonly suppresses testosterone production while increasing cortisol.

The post summarizes a study in the *Journal of Clinical Endocrinology & Metabolism* reporting that higher BMI is associated with lower testosterone, and that obese men had testosterone levels about 30% lower than normal-weight men.

This blog-style article aimed at fitness readers proposes an "optimal" body fat for testosterone and claims a U-shaped relationship. "Your body needs a minimum amount of fat to function optimally. It uses fat to produce key hormones—including testosterone. When body fat gets too low, testosterone production drops off hard… Studies show that both high and very low body fat percentages are associated with reduced testosterone levels, forming a U-shaped curve (Tsai et al., 2013, Mulligan et al., 2006)." The article does not directly cite mechanistic endocrine society guidance, and interprets older observational studies in support of a U-shaped association.

This magazine article discusses recent studies linking fat loss, metabolic health, and testosterone in men. It notes that in a trial with tirzepatide: "They lost more weight, trimmed more from their waists, dropped more fat mass and improved erectile function scores… they also saw the biggest improvements in total testosterone, free testosterone and bioavailable testosterone." The article explains a mechanism: "Fat mass produces aromatase, an enzyme that converts testosterone into oestrogen… the more excess fat you’re carrying… the more opportunity there is for your testosterone to be shunted… In men, that can contribute to obesity-induced hypogonadism – clinically low T driven by poor metabolic health."

In this discussion-thread style post, an anonymous author summarizes lay interpretations of research. "Maintaining a normal to low body fat percentage is generally more beneficial for testosterone levels compared to having a high body fat percentage… There exists an optimal range for body fat… Both very high and very low body fat percentages can adversely affect testosterone levels." The post mixes claims that low body fat does not lead to decreased testosterone with assertions of a U-shaped curve and does not provide primary data; it represents non-expert debate about the issue.