As you get older, your body changes how it gains and loses weight. Both men and women experience a declining metabolic rate, or the number of calories the body needs to function normally. On top of that, women have to deal with menopause. "If women gain weight after menopause, it's more likely to be in their bellies," says Michael Jensen, MD, professor of medicine in the Mayo Clinic's endocrinology division. In menopause, production of the hormones estrogen and progesterone slows down. Meanwhile, testosterone levels also start to drop, but at a slower rate. This shift in hormones causes women to hold onto weight in their bellies. The good news: you can fight this process. Read on.
Caffeine and other stimulants do have a down side though. Since stimulants act upon the central nervous system if used too often or for too long of a time period they can begin to cause overtraining effects. These effects would be much the same as if you were working out too long and too often. This can lead to decreased energy, muscle loss, and ultimately, a lowered metabolism since your body will be trying to preserve energy.
This may explain why the fat-burning effects of eating more protein were confirmed in a study published in the American Journal of Physiology. One group was fed a high-protein diet (just over 1 gram per pound of body weight per day) while the second group consumed an amount closer to the lower recommendation of the RDA (recommended dietary allowance). The group eating the higher-protein diet burned the most fat.