By now you probably know that a high-sugar diet contributes to weight gain by adding calories without adding nutrition (“empty calories”), by increasing appetite and desire for more sugar, and by elevating insulin levels that promote fat storage.

But there are other reasons our bodies like to accumulate fat, so if it seems like the more fat you put on, the harder it is to lose, you’re not imagining things! There are several physiological reasons why losing weight is hard:

Fat cells never go away
When you gain weight, your body creates new cells called adipocytes to store the extra fat, and those adipocyte cells never go away. You can burn away the fat inside, but you can’t burn away the adipocytes themselves. Each adipocyte contains little sensors, and when you burn off the fat inside the cell, those sensors start screaming at your brain to fill them back up. Your brain responds to these signals by turning on the appetite center to find some calories to replenish the missing body fat. The more fat cells you have, the stronger the signals are for your body to replace the fat in the cells, and the more intense your appetite and cravings will be.

In order to avoid this chemical alarm system, you have to lose weight slowly, gradually creeping down your fat levels so as not to arouse the suspicion of the sensors in the fat cells. This is the main reason “crash” diets never work in the long term – losing fat too quickly will trigger all the alarms, resulting in maximum hunger and unbearable cravings.

Homeostasis (the “Set Point”)
Homeostasis (a.k.a. your metabolic “set point”) is a fancy way of saying that your body likes to maintain the level of body fat that it’s accustomed to, and it makes adjustments to your metabolism and your appetite in order to stay that way. Hormones like leptin sense nutrient and fat levels in the body, and signal your brain to adjust your appetite and metabolism to maintain the status quo.

The reason exercise, especially strength training with weights, is vital to a weight loss program is that weight training increases your metabolism and gives your body “permission” to burn off the extra calories you have stored as fat. If you don’t exercise, your body gets stingy and lowers your metabolism when you reduce your food intake, instead of giving up its fat stores.

Yo-Yo Dieting
The process of losing and subsequently regaining weight is referred to as yo-yo dieting. Each time you go through this cycle, it gets harder and harder to lose body fat. Here’s why:

For the sake of example, let’s say your normal caloric intake (your “set point”) is 1600 calories each day. You decide you want to lose weight quickly, so you go on some goofy banana-peel-and-beetle-soup diet that limits you to 800 calories a day. You’re hungry at first, but you stick with the diet for a few weeks and you successfully lose some weight. Congratulations! But by losing weight with this method, you have also lowered your “set point” to 800 calories. When the goofy diet becomes unbearable, you go back to your “normal” eating patterns (1600 calories). Since your metabolism is now set for only 800 calories, the “extra” 800 calories are stored as fat, and within a few weeks, you’re right back to the weight you started at.

There’s more bad news about yo-yo diets: When you lose weight quickly, a lot of the weight lost is lean muscle tissue. When you put the weight back on, it’s fat, not muscle. After a few yo-yo cycles, you have less muscle and more fat than you did when you started, even though you may weigh the same on the scale. Less muscle means a lower metabolism, so even though you weigh the same, your set point is now lower, making it even easier to over-eat and store even more fat!

The key to defeating the yo-yo cycle is to make small nutrition changes over long periods of time – no drastic diets – and to exercise with weights regularly to keep your metabolism elevated. When you make some basic nutrition improvements and work out consistently, you can easily trim a few pounds every month without starving yourself or driving yourself crazy with gimmicky diets.