People who go on extended fasts or fad diets that severely restrict calorie intake will deprive themselves of vitamins, minerals, fibers, and other nutrients their bodies need to function normally.

They may think they’re just losing unwanted fat, but when a body goes into starvation mode — a physiological state that evolved as a defense against famine — it actually protects fat stores and instead harvests calories from lean tissue and muscle.

This can lead to muscle loss and osteoporosis (loss of bone density), and can eventually damage the brain, heart, kidneys, liver, and other organs.

People on diets often deprive themselves of all of their favorite foods, and that sense of deprivation can make it difficult to remain on their diet very long. As a result, a person’s body weight can yo-yo, as they quickly lose weight and then gain it right back.

Central obesity, the fat cells around the waist that people tend to acquire as they age, promotes a heightened inflammatory reaction that attacks healthy brain cells.

When scientists examine the abnormal amyloid plaques found in brains of people with Alzheimer’s, they routinely see evidence of inflammation.

In my book, “The Alzheimer’s Prevention Program,” I provide several anti-inflammatory strategies such as getting daily physical exercise and eating omega-3 fats that come from fish and nuts. These approaches can counter the excess inflammation that results from body fat.

Rather than going on a crash diet, I recommend a nutritious diet that involves reasonable portion control.

Eating several small meals throughout the day (breakfast, lunch, and dinner, plus midmorning and midafternoon snacks), helps people avoid the hunger that sets in when they go too long without food.

It’s helpful to combine healthy carbohydrates and proteins in every meal and snack. The carbohydrates will provide immediate energy while the proteins provide a sustained sense of being satisfied.

Proteins consist of 20 amino acid building blocks, nine of which are termed “essential,” meaning that our bodies can’t make them on their own so we must consume them in our diets.

You can get these essential amino acids from fish, meat, poultry, yogurt, eggs, milk, cheese, nuts, and soybeans.

Drinking plenty of water and tea can help curb appetites, and avoiding processed foods and refined sugars will also aid in losing weight.

Though we all know we should consume healthy foods, sometimes it’s difficult to change old eating habits. In recent years, scientists have identified the areas of the brain that make it hard to break old habits, as well as the brain regions that help us maintain better dietary control.

Researchers at the California Institute of Technology (Caltech) used functional magnetic resonance imaging (MRI) scanning to show that decisions about whether to overeat or to resist doing so take place in the prefrontal cortex — the part of the brain that controls decision-making.

When we overeat or choose unhealthy foods, our brain’s ventromedial region(an area in the middle of the forehead, just above the eyes) is in charge.

But when we resist overeating and make better food choices, the prefrontal lobe’s dorsolateral area (just behind the temples) rules the day.

The good news is that as we make better food choices over time, the prefrontal cortex becomes stronger, making it easier to resist temptation.

In fact, practicing healthy behaviors actually “re-wires” our brains, creating healthy habits.