Fad diets have been around for a long time. Most of them are not new, but have just been recycled and often renamed.

What are fad diets? Fad diets are like a fairy tale. We really want to believe in them. Some people become disillusioned and give up. Others don't want to give up hope and believe the next diet will be the answer to all their weight loss dreams.

Characteristics of fad diets include:

1. A drastic reduction in calories

2. A focus on a certain food or foods (grapefruit diet anyone?)

3. They promise a large amount of weight loss in a short period of time with supposed little effort

4. They don't work.

Let's look at these characteristics one by one.

1. A drastic reduction in calories.

First of all, what is a calorie? A calorie, in the food sense, is a measure of energy: It is the amount of energy needed to raise the temperature of 1 kilogram of water by 1 degree Celsius.

This makes it sound like all calories are the same--that 100 calories of kale is the same as 100 calories of chocolate cake. And in a laboratory setting, this is true. But not in the body. I think we can intuitively sense this.

But the take-home message is that calories are energy. The average recommended daily amount of calories for women is 2,000 and for men 2,500. Obviously some people will need more and some will need less.

So when a person--let's say a woman--drastically reduces her daily caloric intake to 1,000-1200 calories, she is drastically reducing the amount of energy her body has coming in to use. If we look at the (out-dated) calories in/calories out model, it would make sense that if there are fewer calories coming in, that the body would have to get the additional energy it needs from its fat stores.  

But that's not what happens.

What happens is that the body starts perceiving that there is a famine and it will have to get by with fewer calories/less  energy coming in. So it starts by losing some fat. But fat is important to the body. It is more than just a reserve of energy and a source of insulation. It keeps our organs in place, makes some of our hormones, supports cell growth,  communicates with the rest of the body and allows us to absorb fat-soluble vitamins (vitamins A, D, E and K). Fat helps to keep us alive.

And that is the goal of the body--to keep us alive.

If you are reading this, your body is doing a good job. Tell it thanks!

The body does not want to burn all of our fat stores, especially not all at once. So on a very low calorie diet, the body starts 1) to lower its metabolic rate and 2) to burn muscle to help spare fat.

So 1) you are eating fewer calories AND burning fewer calories.

And 2) when you lose muscle, your metabolic rate slows down even further. This is because muscle has a higher resting metabolic rate than fat. Which means that when you are sitting around doing nothing, the more muscle you have, the more energy you will be burning.

 And then,  when you have quit your very low calorie diet  and go back to eating "normally", you will put some weight back on. This weight will be fat--NOT muscle, so your metabolic rate will be lower than before you went on the diet! How is this helpful?

It's not.

You have tortured yourself and your body to lose weight to be "healthier" ( and okay, to look better) but you have ended up worse than before you started!

More  on how to lose weight successfully.

Next we'll discuss how fad diets focus on certain food (s) to the exclusion of others.