1,000-calorie "detoxes." Meal replacements that provide barely enough energy to function. The National Institute on Aging confirms that maintaining a healthy weight remains achievable with age-appropriate strategies, even as physiological changes occur. The same meal your body handled efficiently at 30 produces a stronger fat-storage signal at 45.
If you’re at above 12% fat, then, by all means, use a slight calorie deficit in order to get to 8-12% body fat levels and then once you get there, continue with maintenance calories or bounce around between slight deficit and slight surplus (mini cut/bulk cycles, etc). When you consume fewer calories than your body burns, the physiological consequences extend well beyond fat loss — hormone production, including testosterone, can be affected. If you need to lose body fat, moderate deficits of 300 to 500 calories preserve more hormonal function than crash diets.
This CR-mediated reduction in sex hormones is consistent with that seen in long-lived CR rodents, and further support the concept that many of the hormonal adaptations to CR are remarkably well conserved among species (Grewall et al., 1971; Howland, 1975; Merry & Holehan, 1981; Govic et al., 2008). Relationship between serum SHBG concentration and BMI (upper left panel), ISI by Matsuda and De Fronzo (upper right panel), serum IGF-1 concentration (lower left panel), and serum adiponectin concentration (lower right panel) in the study subjects. Mean values for body weight and BMI were significantly different between the three groups (Table 1).
However, this seemingly harmless practice can lead to serious health consequences, particularly regarding testosterone levels. Diet-related testosterone suppression is typically functional and reversible — it resolves when energy intake is restored and is not the same as clinical hypogonadism, which is a persistent medical condition requiring diagnosis and treatment. It is important to note that routine, moderate calorie restriction in otherwise healthy adults is not established as a cause of clinically significant hypogonadism. In women, the hormonal consequences of severe calorie restriction more commonly manifest as menstrual irregularity or amenorrhoea — a recognised feature of RED-S. It is important to note that many of these symptoms overlap with general caloric restriction, overtraining syndrome, and other nutritional deficiencies (such as low iron, vitamin D, or zinc), so they are not specific to testosterone alone. Because testosterone decline is often gradual, symptoms can be subtle at first and are frequently attributed to the general fatigue of dieting rather than a hormonal shift.
A multicenter randomized controlled trial of the effects of 2 yr of 25% CR in middle-aged non-obese (body mass index ≥ 22 and 2) women and men, currently in progress (CALERIE phase 2), might provide some of this information regarding a cause-and-effect relationship, and the time-course of these CR-mediated hormonal adaptations. First, because of the cross-sectional design of our study, we are only able to show associations with diet, physical activity and circulating sex hormones, and cannot determine true causal relationships. In the present study we found that long-term CR without malnutrition does not protect against a decline in DHEAS in humans as there were no differences in serum DHEAS concentration between the individuals practicing CR for an average of 7 years and age-matched controls. In gorillas, chimps and human primates, the sex steroid hormone DHEAS, which is produced by the adrenal cortex, circulates in far higher concentrations than any of the other endogenous sex steroid hormones in serum (Hornsby, 1995). More studies are needed to elucidate the role of a reduction in anabolic hormones (e.g. testosterone and 17-β-estradiol) in combination with the reduction of other growth factors (e.g. insulin and IGF-1) and inflammatory cytokines (e.g. IL6) in mediating the anti-cancer effects of CR. When food intake is reduced, cell growth and proliferation decrease as a result of lower availability of substrate and energy.