A problem that adds to the confusion is the simple fact that cutting back on carbohydrates works, at least for a quick drop in body fat and body water. The piece of the puzzle missing for most dieters is the long-term effects on the body due to such a drastic reduction in carbohydrates.

In case you haven't heard the latest scoop on the high-fat, low-carbohydrate diet, let me fill you in on the concept.

This diet was very popular during the 70s and was popularized by Dr. Atkins. Like many diets of the past, this one gained a lot of press. After a couple of years of popularity Dr. Atkins' dieting approach fell by the wayside for several reasons.

Unfortunately, the low-carbohydrate, high-fat diet is back, and seems to be gaining in popularity once again. Currently, Dr. Sears' book The Zone and another called Protein Power have revitalized the Atkins' diet.

The concept is that a person should eat more protein, more fat and very little carbohydrate as the day wears on. Because the dieter is eating more fat, they tend to feel full longer, and this helps the person exert more control over hunger.

In the past, people were allowed to eat as much red meat as desired, but had to keep their carbohydrate intake as low as possible. This combination of foods causes a chemical reaction, thereby causing the person to burn body fat at an accelerated rate.

It's called a ketogenic diet. The low intake of carbohydrate, coupled with a high-fat diet and exercise causes the production of ketones. Ketones are the chemical residue of broken-down fats in the blood.

To be more specific, if insufficient carbohydrates exist, the body begins to mobilize fat to a greater extent than it can use.

The result, both at rest and after exercise, is incomplete fat metabolism and the accumulation of acid by-products called ketone bodies. This situation can lead to a harmful increase in the acidity of the body fluids, a condition called acidosis or ketosis.

The ketogenic diet was conceived in the 20s by doctors in France and the United States. They discovered that prolonged starvation promotes ketosis as the body uses its fat reserves. So, they devised a way to mimic the chemistry of starvation through diet.

The current diet revolution is nothing new, it's just an adaptation of these old concepts. The problem is, most people get their information from uninformed sources which fail to understand the scope of their recommendations.

If you've started a higher-fat, lower-carbohydrate diet then there are a few things you should know:

1) By reducing carbohydrates you will see a drop of body weight and body fat. However, if you drop them too low while exercising, you could alter your body's T3 levels.

T3 is an active thyroid molecule that helps regulate your metabolic rate. Diets low in carbohydrate tend to cause a reduction of T3, which in turn can slow down your metabolic rate. This is particularly true for people who under-eat and over-exercise.

2) A lot of the weight you drop while on a low-carbohydrate diet is water weight. For every gram of carbohydrate you ingest, about three to five grams of water usually accompany it. By decreasing your carbohydrate intake you naturally drop body water.

Although this may sound like a good idea, when you resume eating carbohydrates you may find that your body rebounds and retains excess water. The water retention will dissipate after several days, but it wreaks havoc on the dieter's mental state.

3) During the 70s, clinicians began noticing that people that followed the Atkins' diet regained their weight very rapidly once they ceased the diet. In fact, they found the longer a person had been on the low-carbohydrate diet, the more carbohydrate sensitive they became.

Further, when this diet was combined with exercise it caused people to become even more carbohydrate sensitive. This could be the devastating pitfall, because once the low-carbohydrate diet has ended, and the person tries to resume eating carbohydrates, his body tends to horde and store the carbohydrates as opposed to using them for energy.

The person notices a fast accumulation of body water that's followed by an abnormally fast body fat gain. Although the water weight will eventually drop off, the person notices that he gains body fat very easily, but loses it more slowly in the future.

4) Carbohydrates provide a 'protein sparing' effect. Under normal circumstances protein serves a vital role in the maintenance, repair, and growth of body tissues. When carbohydrate reserves are reduced the body will convert protein into glucose for energy.

This process is called gluconeogenesis. The price that's paid is a reduction in the body's protein stores. In other words muscle! All, in turn, causes the metabolic rate to slow down as well.

5) There's another problem that eating too little carbohydrate creates. Your muscle fullness depends to a large extent on your carbohydrate intake. Low carbohydrate levels tend to make muscles lose their density and flatten out.

Carbohydrates are a great source of fuel, so not eating enough can lower your energy level and make your muscles feel softer.

6) These diets focus on the relationship between carbohydrates and insulin (a hormone that shuttles fuel into fat). However, their suggestion that insulin exerts negative effects is not only misleading, it's downright flawed.

Insulin does play a role in fat storage, but it also causes glucose to be shuttled into muscle cells as well. Our diets should keep blood levels of insulin as stable as possible, not try to suppress its release.

7) On the flip side, you'd have to be totally out-of-the-loop if you haven't heard that more fat increases your risk of heart disease, cancer, and obesity. Naturally, everyone wants to hear that they can eat fats and lose weight. I guess if you want to look good in your coffin, then it's okay with me.

I've always disagreed with the American Dietetic Association and the idea that 30 percent fat is healthy. I believe that a diet of 20 percent or less fat poses a substantial health benefit as well as a reduced risk of obesity.

It amazes me that this diet is back. Are people's memories really that short that they can't remember the reason that the Atkins' diet vanished the first time?

Consider what bodybuilders learned years ago. During the 70s and early 80s, every major bodybuilding competitor dieted on a low-carbohydrate, high-fat diet, yet most of them ended up very smooth and not very well defined.

The bodybuilders of the late 80s and 90s have improved dramatically. By having a diet high in protein, low fat, and moderate in carbohydrates, some of the best physiques ever have been produced.

Some confusion about carbohydrates could stem from the fact that people see and hear bits and pieces of information from gym buddies and accept the information as fact.

While it is true that as a contest nears bodybuilders decrease their carbohydrates, that doesn't mean that cutting back excessively yields better results.

Over the years I have found that by removing the starch at the final meal during the last three to four weeks before a show, bodybuilders tend to get very tight and more defined. And for others, a biased article designed to sell books placed prominently in a major magazine could be all it takes to attract everyone's attention.

When you hear people talking about a 'new' diet approach, stop and ask yourself does it follow healthy guidelines? Does the diet call for measures that you cannot do for life? If so, don't even try it.

For 18 years Keith Klein has been one of America's leading nutritionists. His books include Weight Control For Young America, Lean For Life, Get Lean, The Healthy Chef, and Kidtrition Cafe. His columns run in Fitness Express, Health and Fitness, and many other publications.

Keith hosted a nationally syndicated 2-hour radio program GetFit, for three years on Prime Sports Network. Keith's popular television show, Smart Bodies, aired weekday mornings on TPN for several years. He currently hosts the Keith Klein Nutrition Hour and is director of The Institute of Eating Management, where he acts as personal nutritionist to many of America's top athletes, models, and dancers, including Mary Lou Retton, Kim Zmeskal, Ricky Sanders (Washington Redskins); golf pros Greg Chapman and Kelly Knehne; Lee Labrada (Mr. America & Mr. Universe), Carla Dunlap (Ms. Olympia), Victoria Gay ('Jazz' of the American Gladiators), Betsy Bates (Ms. America), Tatianna Anderson (Ms. Fitness USA), Deanna Clark.