Obesity is a risk factor for cardiovascular disease and is associated with many comorbidities, including type 2 diabetes, hyperlipidemia, heart failure, and hypertension. Being even moderately overweight can limit your mobility, leading to falls or strains in everyday life and it may even lead to a decline in self-esteem. Obesity is also associated with decreased life span and mortality. However, there is also evidence that mild obesity in this elder age group is associated with a lower, not higher, risk of death- a finding termed the obesity paradox.

Obesity is the excess accumulation of body fat. The BMI, or, weight in kilograms divided by the square of the height in meters, correlates fairly well with body fat stores and is generally used to classify medical risk. However, the BMI can classify some older people as overweight (BMI 30.0–34.9 kg/m2) or obese (BMI ≥ 35.0 kg/m2) who actually do not have an excess of body fat. For example, if a person loses height as a result of vertebral compression fractures, his or her BMI would become higher, even with no change in weight or body fat. On the other hand, changes in body composition with age, including loss of muscle and an increase in fat, may not be reflected in the BMI, even if the person really does have too much body fat.

With age comes sarcopenia. It is known as the progressive loss of muscle mass, primarily skeletal muscle, resulting in a decrease in strength and power. The process begins as early as the 20s or 30s. Progressive loss of skeletal muscle with age, along with an increase and redistribution of body fat, is known as sarcopenic obesity. This type of obesity is associated with higher morbidity and mortality rates as well as a decline in functional strength, which leads to frailty. This loss of muscle mass may go unnoticed in an older person until he or she begins to lose physical function. In an older person with sarcopenic obesity, the BMI may mislead because of the high percentage of fat and the low lean mass.

This change in body composition with age is a result of several factors. Illness or inactivity can lead to loss of muscle, while body fat is preserved. The combination of reduced physical activity, a lower resting metabolic rate, and an unchanged intake of food can increase the likelihood of sarcopenia. As people age, their physical activity tends to decrease, resulting in muscle loss. As muscle mass decreases, the amount of available insulin-responsive tissue is reduced, resulting in insulin resistance, which in turn promotes the metabolic syndrome and an increase in fat.

In general, obesity in younger adults has been shown to shorten life expectancy. In older people, the effect of obesity is much more complex. The optimal weight in terms of survival increases with age. For those over age 75, the relative risk of death from all causes and from cardiovascular disease has been found to decrease with increasing BMI. The relationship between BMI and death from all causes in older adults may actually be a U-shaped curve, meaning that the risk of death rises at both extremes of BMI values.

Researchers are not exactly sure why excess weight protects older adults, but some theorize that, as we age, the presence of nutritional and metabolic reserves are advantageous. It is thought that if you were to develop an illness, a little more reserve gives you a greater chance to recover from that illness, For example, if you were to develop cancer and need to undergo chemotherapy, which can lead to rapid weight loss, you would have extra reserve to help you through the illness. With extra reserves, you might be able to recover from stresses such as surgery or a common illness such as pneumonia.

The gist is that you don't need to worry about being slightly overweight, as long as that extra weight is maintained at a consistent level. It is still emphasized by researchers and physicians that exercise for most people positively affects health, and that no one who is at a healthy weight or slightly overweight should intentionally gain extra weight in the hopes of warding off disease or extending their longevity. It is still very much a fact that being very overweight is detrimental to health, and exercising to lose body fat and to gain muscle mass is always beneficial. Always speak to your physician before deciding a weight loss plan is for you. Your doctor knows your medical conditions and medication regime and can best direct you.

Source: https://www.mdedge.com/ccjm/article/96020/geriatrics/obesity-elderly-more-complicated-you-think/page/0/3