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Why do many people have difficulty losing weight?

This is an excerpt from Practical Guide to Exercise Physiology 3rd Edition With Web Resource by Robert Murray,W. Larry Kenney.

In one sense, losing weight can be as easy as moving more and eating less. For some people, it is that easy. After all, the laws of thermodynamics cannot be broken. If you consistently ingest fewer calories than you expend, you will lose weight over time. Yet for many people, moving more and eating less does not have the same satisfying results. Why is that? There are many factors that affect weight loss, as summarized in figure 7.5, and this section discusses in more detail some of the individual variations that occur. It is important to remember that losing weight and then maintaining that weight loss often require two different approaches. In brief, losing weight is best accomplished by an emphasis on reducing caloric intake, while an emphasis on increased physical activity appears best for maintaining that weight loss.

GENETICS

Genes are pesky things. Some scientists think genes determine body weight and make futile any attempt to establish a new body weight outside of a fairly narrow gene-determined range. Other scientists agree that genetics plays a role in body weight but not as the sole determining factor. Otherwise, how do you explain people who lose hundreds of pounds and maintain their new lower weight for decades? The current thinking is that genetics does play a role in making some people susceptible to obesity, with physical activity and diet being the predominant factors in determining the rate and extent of weight gain. To be clear, once a person becomes obese, it is very difficult—but not impossible—to establish a healthier body weight.

HOMEOSTATIC COMPENSATION

This sounds more complicated than it is. The thinking on homeostatic compensation is that your body establishes a set point for body weight and then fights against any attempts to alter body weight.

As a simple example, people who introduce exercise into their daily routine in an attempt to lose weight are often frustrated by the slow pace of weight loss. Research shows that when people begin to exercise regularly, they often increase their food intake and decrease their physical activity during the rest of the day, slowing the rate of weight loss.

Consistently undereating reduces resting metabolic rate (RMR), the thermic effect of food (TEF), the energy cost of movement (due to weight loss), nonexercise activity thermogenesis (NEAT; posture, fidgeting), and satiety hormones (e.g., leptin, insulin, cholecystokinin), while hunger hormones (e.g., neuropeptide Y, ghrelin) are increased. In other words, undereating results in compensatory metabolic and behavioral responses that combine to work against weight loss. Those responses do not make it impossible to lose weight, but they can make it more challenging to do so.

HORMONES

The neuroendocrine system (brain, central nervous system, hormones) plays an important role in the regulation of hunger and satiety. Eating provokes the release of dozens if not hundreds of hormones from the brain, gut, pancreas, liver, and other organs, creating a rich mix of signals that influence feelings of hunger and satiety. Some people may be more sensitive to those signals than others, and that higher sensitivity means their hunger is turned off sooner, so they eat less and do not gain weight. On the other hand, if you are less sensitive to those hormones, you may continue to eat and consume excess calories. Yet another twist in this story is how the body prioritizes the oxidation of the nutrients consumed. Alcohol usually has top priority for oxidation, followed by carbohydrates, amino acids, and fat. If—for whatever reason—there is a metabolic shift away from the oxidation of alcohol, carbohydrates, and amino acids, more fat will be deposited. Scientists continue to research this and other theories that might lead to weight gain and obesity.

MENOPAUSE

The loss of estrogen and progesterone during and following menopause has various metabolic effects that often lead to weight gain, a change in the distribution of fat, and a loss of lean body mass. At the same time, daily physical activity tends to decrease. Consequently, the risk of type 2 diabetes and cardiovascular disease rises. Women who are physically active before and during menopause fare better afterward; they gain less fat (particularly in the abdomen), retain more muscle, have better blood flow, benefit from less inflammation, and have stronger bones. Many women can spend 30 years or more in postmenopause, so continuing regular physical activity, including resistance exercise, and eating a healthy diet are essential to reduce the risk of metabolic dysfunction and android obesity.

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