Where does weight go when you lose it?

DEAR DR. ROACH: When you lose weight through diet and exercise, where does the weight go?

ANSWER: Weight gain and weight loss in the very short term can be related to body fluid, but I think you are really talking about people who have made a long-term loss of, say, 10 pounds.

Those 10 pounds can be fat or muscle. In people who are eating very few calories and not exercising, it will be a combination of both of these body components.

Unfortunately, losing muscle is unhealthy, which is why it’s best to exercise in combination with changing the diet, so that the weight loss is all fat. I’ve had patients who have lost fat and gained muscle, who can be frustrated that their weight isn’t going down, but in reality they are much, much healthier.

From a physics standpoint (the study of medicine starts with physics and chemistry), a pound of fat represents about 3,500 calories. Eating 3,500 more calories than you expend means a pound of fat gain, while the reverse means a pound of weight loss. In weight loss, the fat is used to provide energy for the body's metabolic processes and is (almost literally) burned away into carbon dioxide.

However, physics doesn’t properly address the complexity of weight gain and loss in humans. Simply eating less and exercising more doesn’t lead to the expected weight loss, as the body has ways of adapting to lower food intake. Also, as people lose weight, their energy needs decrease further, and the ‘3,500 calories per pound’ rule becomes a very poor approximation. Finally, the processes controlling eating behavior are complex, and in some people, the body uses every trick it can, including overpowering hun-ger, to stay at the same weight.

For these reasons, I don’t find simply telling people to eat less and move more to always be an effective therapy. DEAR DR. ROACH: Seventy-five-plus years ago, authorities said to avoid cooking with aluminum. As I understand it, aluminum deposits are found in the brains of those who have died from Alzheimer’s disease. I realize that modern science makes no connection with this (so far), but it's pretty easy to avoid aluminum. My mother died from Alzheimer’s and had been cooking with aluminum for at least 45 years

ANSWER: Aluminum was of concern, especially back in the 1980s and ’90s. However, it is no longer thought that using aluminum utensils or cookware affects Alzheimer’s risk.

In a previous column, I discussed what can be done to reduce risk of dementia. I did not include quitting smoking, but that may be the most important factor for a person who is still smoking.

Keith Roach is a syndicated advice columnist and physician. Contact him by email at: ToYourGoodHealth@med.cornell.edu