For many people, perhaps the most noticeable side effect of a falling testosterone level will be an expanding waistline. Just as increasing cortisol levels can lead to excess belly fat, so can declining testosterone levels—and when you have both occurring simultaneously (cortisol rising and testosterone falling) it is virtually inevitable that weight gain will follow.
One study, published in 1996 in the Journal of Clinical Endocrinology and Metabolism, showed that obese women who boosted their testosterone levels lost significantly more abdominal fat and gained more muscle mass compared to women who were given a placebo and whose testosterone levels remained suppressed. This was more than a decade ago—and still most doctors and health professionals view testosterone strictly as a “male” hormone, when the reality is that while women certainly don’t want “male levels” of testosterone, they definitely want to maintain what they have.
The scientific literature in support of maintaining normal youthful testosterone levels (versus allowing them to fall in the face of stress and aging) is at least as strong as the research in support of maintaining normal youthful cortisol levels (which rise in response to stress and aging). Here is a sampling of some of the available studies:
•Austrian medical researchers have shown that weight loss from dieting results in a significant reduction in testosterone levels in overweight women. But this effect is largely due to a high level of dieting stress caused by excessive calorie restriction (which elevates cortisol) and unbalanced with exercise (which could maintain testosterone levels). Researchers from Penn State University have shown that weight loss induced by diet alone leads to a significant drop in testosterone and fat-free mass (muscle)—an effect that can reduce metabolic rate and make weight regain easier.
- •Scientists from Northwestern University, in Chicago, have shown that weight gain in young men (ages twenty-four to thirty-one) was significantly related to low testosterone levels, with a graded relationship between the lowest testosterone levels and the greatest degree of weight gain. In a related series of studies, researchers at Cornell Medical College, in New York, found that the age-related decrease in testosterone is significantly exacerbated in overweight men with the metabolic syndrome. As testosterone drops, body weight goes up—and the drop in testosterone and the rise in weight are more pronounced in men who have metabolic syndrome than it is in men without. (Men who don’t have the condition also gain weight as testosterone drops, but to a less severe degree.)
- •As part of the Massachusetts Male Aging Study (which followed over seventeen hundred men, ages forty to seventy), researchers at the New England Research Institutes found that overweight men had significantly lower testosterone levels and a greater rate of decline compared to normal-weight men of any age. Endocrine researchers from Venezuela have found that testosterone levels are lower in overweight men ages twenty to sixty, and that there is a graded and proportional relationship between low testosterone and weight gain (the fattest men had the lowest testosterone).
- •Norwegian medical researchers have shown that the lowest levels of testosterone are found in men with the most pronounced central (abdominal) obesity. In addition, those with lower testosterone also had higher blood pressure and increased rates of diabetes. These findings suggest that testosterone may have a protective effect against weight gain and development of diabetes and hypertension.
- •In a very important study from researchers in aging at the University of Florida, the incidence of low testosterone in a general population of men over age forty-five was estimated to be 38.7 percent. Those with low testosterone were about twice as likely to also be overweight and have hypertension, high cholesterol, and diabetes.
- •In a study from researchers at the Albert Einstein College of Medicine, in New York, overweight men were shown to have reduced testosterone levels, with the lowest levels seen in men who continued to gain weight over time (eight years follow-up). Interestingly, the level of testosterone was found to predict subsequent weight gain: Lower testosterone related specifically to increased weight gain in the abdominal area.
- •Australian scientists at the University of Adelaide have shown that testosterone levels decline with aging even in healthy men—and also lead to obesity and metabolic syndrome.
- •Italian hormone researchers have shown a negative relationship between C:T ratio and obesity in men and women. As stress-related cortisol levels rise, testosterone levels drop in both sexes, leading to weight gain, especially within the abdominal area.
- •Public-health researchers from Hong Kong have shown that age-related declines in testosterone are associated with increased levels of abdominal fat and higher rates of the metabolic syndrome. In a series of studies, low testosterone levels explained 35 percent of the variance in metabolic syndrome rates (more metabolic syndrome equated with lower testosterone).
- •Brazilian medical researchers have found low testosterone levels to be strongly associated with weight gain and specifically with higher abdominal fat (waist-to-hip ratio). Norwegian researchers have shown that the lowest testosterone levels are found in subjects with high waist circumference, even when their total level of body fat is rather normal, suggesting that waist circumference (abdominal fat) is the preferred anthropometric measurement to predict testosterone levels (bigger waist = lower testosterone).
- •Health researchers from Oklahoma State University have demonstrated a direct effect of testosterone on adipose tissues (fat cells) and obesity, showing that testosterone leads to an increase in lipolysis (fat breakdown). Normal testosterone levels lead to a normal distribution of body fat, but as testosterone levels decrease in response to stress and aging, there is a tendency to increase central obesity (gain abdominal fat). In fact, bringing testosterone levels back to within normal ranges in older men and women has been shown to reduce the degree of central obesity.
- •Researchers at the University of Washington, in Seattle, have shown that among women who lose weight using dietary restriction alone, each 2 percent loss of body weight is associated with a fall in testosterone levels of 10 to 12 percent.