Examining the Effects of Calorie Restriction on Testosterone Concentrations
Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.
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Calorie restriction has been demonstrated to significantly decrease chronic low-grade inflammation throughout the body, which is a primary factor behind many diseases including cardiovascular and cancer conditions. Furthermore, studies have also demonstrated its effect in reducing testosterone levels among obese men.
However, this effect can be reversed with adequate food intake; excessive exercise combined with decreased energy intake may create a state of relative hypogonadism among athletes and those who employ an extreme exercise regime.
The Endocrine System
The Endocrine system is a network of glands that produces hormones to facilitate communication among cells.
It controls almost every function and cell in your body - including growth, development, metabolism and composition of bodily fluids such as blood sugar levels or salt concentration.
Furthermore, reproduction and sexual development also involve its presence and participation; its main constituents include hypothalamus pituitary gland adrenal glands thyroid gland and male gonads (ovaries and testes).
Hormones are molecules that transmit signals between cells, telling them what to do. Hormones are released by glands in response to specific stimuli and travel through the bloodstream to their targets cells.
Most hormones only target certain types of cells such as those within specific organs; some hormones like insulin may have many. Hormones are released pulsatilely so their concentration in target cells remains controlled.
Communication within the endocrine system is extremely intricate; usually one gland stimulates another gland to produce and secrete hormones or vice versa.
Hypothalamus plays an integral part in stimulating and suppressing pituitary hormone release. Additionally, its own hormones (such as melatonin) also have an impact on its operations. The hypothalamus secretes hormones to control water balance and sleep patterns, signalling when to produce other hormones like growth hormone.
Ovaries and testes produce and control their own hormones such as estrogen and testosterone production respectively.
Testosterone
Testosterone is an essential steroid hormone responsible for regulating multiple bodily functions, including muscle growth and sexual function.
Normal levels of testosterone typically range between 300 to 1,000 nanograms per deciliter of blood. Any deviation below this range has been linked with symptoms including loss of libido, fatigue and depression (known as hypogonadism).
While minor fluctuations within this range are unlikely to have clinical ramifications, persistent decreases may cause problems related to sex drive or fertility issues.
Environmental Factors
When considering how dietary choices influence testosterone concentrations, it's essential to factor in the entire hormonal environment in which testosterone production occurs.
This includes the central hypothalamic-pituitary-gonadal axis which controls androgens within the body - testosterone being one key anandrogen which regulates energy expenditure, bone density and blood glucose regulation among many metabolic processes.
Testosterone levels can be affected by various factors, including diet, exercise and genetics. Higher testosterone concentrations have been linked with greater muscle mass and less body fat. Conversely, lower testosterone concentrations have been associated with obesity and diabetes mellitus.
Dietary Intake and Testosterone
Researchers in the US and Belgium conducted a meta-analysis of randomized controlled trials to ascertain the effect of diet on serum testosterone, concluding that low-fat diets could boost levels by improving testicular gland function and decreasing aromatase conversion into b-estradiol by adipose tissue.
Another key indicator of diet effectiveness is its capacity to reduce adipose tissue. To examine this point, a study investigated the effects of a low-fat, calorie-restricted diet on this indicator. An accumulation of this type is one major contributor of insulin resistance and type 2 diabetes mellitus.
Long Term Calorie Restriction
Long-term calorie restriction has been shown to significantly reduce sex hormones in laboratory animals, yet little is known about its effect on humans.
To address this question, circulating concentrations of total and free testosterone, 17-b-estradiol, SHBG and dehydroepiandrosterone sulfate (DHEA-S) were measured in 24 men who participated in long-term severe CR with adequate nutrition, along with age- and body fat-matched endurance runners as well as non-obese sedentary individuals consuming Western diets.
Serum levels were significantly lower while serum SHBG concentration significantly higher among CR group individuals consuming Western diets.
Researchers conducted another study analyzing the relationship between popular diets and sex hormones among 3,128 men between ages 18 and 80 who participated in a nationwide health survey and reported their eating habits, two-day dietary histories, serum testosterone measurements, and reported their daily dietary history for two days prior to receiving their measurement results.
Their results suggested that men who consumed low-fat diets had lower testosterone levels than those eating standard American fare. However, due to being too small a sample size they noted it is too early to draw definitive conclusions regarding which effects one diet might have on sex hormone levels.
Researchers noted that the calorie-restricted diet had an adverse impact on the production of sex hormones by testicles, pituitary glands and hypothalamus. Furthermore, they observed reduced cortisol levels - an androgen precursor - as a result of its consumption. They believe this to be caused by suppression of PLA2G7 gene that regulates testosterone production.
This study suggests that men at or near their ideal weight may require reduced protein consumption to maintain testosterone levels, with an emphasis on maintaining an abundance of nutrient dense foods in their diet and limiting carb consumption which can result in decreased testosterone.
Researchers conducted an investigation on the effects of seven days of food restriction in male judo athletes preparing for national competition, and found it significantly decreased proinflammatory cytokines and hormone levels (IL-6 and TNF-a responses during Single Joint Jump Task Test (SJFT), increased testosterone production while decreasing cortisol levels.
They theorize this may have been driven by both exercise and diet changes combined.
Another study investigated the effects of a low-calorie diet (CR) on serum testosterone and sex hormone-binding globulin (SHBG) levels in healthy lean adults, and discovered it led to lower total and free testosterone concentrations and higher SHBG concentrations compared with body fat-matched endurance runners and nonobese sedentary individuals consuming Western diet (WD).
This suggests that, like long-lived CR rodents, long-term CR with adequate nutrition reduces circulating sex hormone levels in humans too.
Furthermore, in obese men, following a low-calorie diet was associated with an even greater increase in testosterone than for normal-weight subjects and improved sexual function and relationship subscale scores.
This effect may be explained by improvements to testicular function as well as reduced conversion of testosterone to b-estradiol in fat tissue.
Conclusions
Examining the effects of calorie restriction on testosterone concentrations is no simple task, as many factors can impact sex hormone levels such as sleep duration, physical activity level and eating habits.
Long-term calorie restriction leads to lower testosterone levels for both humans and animals. Biosphere 2's two year study on human calorie restriction beginning September 1991 demonstrated this fact by significantly cutting cholesterol and blood sugar, in addition to other changes seen similar to laboratory animal research studies of aging and sexual hormones.
As much attention has been devoted to understanding how exercise intensity and duration affect circulating concentrations of testosterone, far less has been dedicated to studying how energy and nutrient intake impacts circulating concentrations of this hormone.
It is likely due to changes in dietary practices affecting many other aspects of health besides just hormonal production (carbs, proteins, micronutrients).
Recent analysis of 5 randomized controlled trials (RCTs) that evaluated the effect of reduced caloric intake on testosterone and other hormone levels found that, on average, decreasing fat consumption significantly raised testosterone levels.
It should be taken with caution, however, because RCTs differed greatly in terms of participant ages, BMIs, energy intake or deficit and length of intervention.
Changes in testosterone and other hormone levels are normal. While fluctuations may occur within their usual range, when levels consistently fall below 300 ng/dL symptoms such as low libido, erectile dysfunction, fatigue or loss of muscle mass may arise - this condition is known medically as hypogonadism.
