Secondary Logo

Journal Logo

Fad diets: Slim on good nutrition


HEALTH MATTERS: Promoting health and wellness: NEW

AMERICANS ARE eating more than ever—and it shows. (See Is Your Patient Overweight?) To shed pounds, many overweight people turn to fad diets designed to help them lose a lot of weight fast. Do they work? And more important, are they safe and nutritionally sound? For answers, let's evaluate some popular fad diets so you can assess the risks and help patients find healthier ways to lose weight. (See How to Spot a Fad Diet.)

Back to Top | Article Outline

“Get thin quick” schemes

Promoters of fad diets promise dieters that they can drop weight quickly and easily, but their claims are rarely supported by respectable research. You may need to warn dieters to be suspicious of diets that sound too good to be true. Here's the skinny on some of the most popular fad diets, including why they may be unsafe.

  • High-protein, low-carbohydrate diets, such as the Atkins diet, are popular and controversial. These diets are extremely high in fat and offer very limited food choices because entire food groups, such as fruits and vegetables, may be eliminated.
  • How they work: With these diets, ketosis is the key to losing weight—but not to healthy nutrition. When the body is starved of carbohydrates, it burns its fat stores for fuel instead of burning glucose. And the by-product of fat breakdown is ketones. When excessive ketones are produced, the kidneys have to work harder to filter them. The body goes into starvation mode and metabolism slows down. Then carbohydrates are burned more slowly, and stored carbohydrates that aren't burned for fuel are converted to fat.
  • Limiting carbohydrates means fewer calories are consumed, which leads to weight loss. Eating lots of protein, which tends to be high in fat, makes people feel full so they may eat fewer calories overall.
  • Drawbacks and shortcomings: The by-product of protein metabolism is nitrogen. Too much nitrogen excretion can damage the kidneys. Excessive protein intake also can boost uric acid production, which can cause gout and kidney stones.
  • Because these diets are low in carbohydrates, they lack some essential nutrients. For instance, they don't have the phytochemicals found in fruits and vegetables, which reduce the risk of cancer. These diets also lack vitamins and minerals, and they pull calcium from bones.
  • The American Heart Association says that these kinds of diets can raise cholesterol levels because of increased fat and decreased fiber and that these diets increase the risk of heart disease, stroke, and diabetes.
  • High-protein, low-carbohydrate diets can produce rapid weight loss. But if a dieter goes back to eating carbohydrates, the body turns much of the food into fat to prepare for another episode of starvation. So people who quit the diet may gain weight more quickly than ever.
  • The Sugar Busters' diet steers dieters away from refined sugars and other carbohydrates with a high glycemic index. Foods with a high glycemic index raise blood glucose levels quickly and foods with a low glycemic index raise blood glucose levels much more slowly. The theory is that eating high glycemic index foods causes a glucose spike, followed by a big drop in glucose levels that stimulates a craving for more high glycemic index foods, resulting in obesity.
  • This diet calls for consuming 30% carbohydrates, 30% protein, and 40% fat. Along with most sugar, banned foods include white bread, pasta, white rice, potatoes, corn, beets, carrots, and bananas. Small portions of whole grains are permitted.
  • How it works: Daily caloric consumption amounts to about 1,200 calories, so dieters tend to lose weight because they're eating fewer calories.
  • Drawbacks and shortcomings: This diet restricts many foods containing essential vitamins and minerals. Also, dieters are less likely to stick with a diet that permits very little sugar.
  • The Eat Right for Your Type (ERFYT) diet is based on the theory that people should eat certain foods that are compatible with their blood type. The originator of this diet claims that when people with certain blood types consume some foods, substances from the food called lectins circulate in the bloodstream and cause blood cells to agglutinate or clot. He thinks that this clotting then causes other problems, such as liver and kidney troubles. The ERFYT diet is supposed to make the dieter healthier by eliminating lectins, but this is unsubstantiated by research. When weight loss occurs, it's because fewer calories are being consumed.
  • The diet is further based on the theory that the earliest people had type O blood. To adhere to this diet, people with type O blood should eat a high-protein, low-carbohydrate diet because our caveman ancestors ate mostly meat. Because type A blood supposedly evolved next, people with type A blood should eat a mostly vegetarian diet with small amounts of protein. People with type B or AB blood may eat a varied diet.
  • How it works: Only those with type O blood seem to lose weight with the diet, possibly because of ketosis as in other high-protein, low-carbohydrate diets.
  • Possible drawbacks and shortcomings: Unless the dieter has type O blood, the diet doesn't help with weight loss. The diet for those with type O blood has the same dangers as other high-protein, low-carbohydrate diets. Also, little published evidence supports the notion that digested food attacks and agglutinates blood cells, the diet's premise. Because blood from early man hasn't been preserved (and blood types were discovered only in the early 1900s), the claim that blood types evolved isn't supported by evidence.
  • The Zone diet advocates eating 40% carbohydrates, 30% protein, and 30% fat.
  • How it works: If this diet works, it's probably because the daily caloric intake is low, ranging from 1,000 to 1,600 calories/day.
  • Drawbacks and shortcomings: Because this low-carbohydrate diet puts the body into a state of ketosis, it has many of the same drawbacks as the other high-protein diets. As with most other fad diets, no scientific studies support this one.
Back to Top | Article Outline

How you can help

Teach patients who want to lose weight to avoid ineffective and potentially dangerous weight-loss schemes, especially if these diets are used for more than a couple of weeks. Remind them to use common sense. These interventions can help:

  • Provide available resources. Distribute educational materials to patients, including the food guide pyramid and resource guides from the Food and Drug Administration, The National Institutes of Health, and the American Dietetic Association.
  • Assess your patient's eating habits and be alert for clues that she's following a fad diet. Educate her about the dangers of fad diets and urge her to lose weight by following a nutritionally sound diet and exercising more.
  • If she's overweight or obese, help her make major lifestyle changes that will help her keep weight off. For example, consult a dietitian who can help her plan menus. Discuss the importance of controlling portion sizes and calorie intake.
  • Help her set realistic weight-loss goals, such as losing a pound or two a week. Encourage her to join a support group. Caution her to be suspicious of diets that are making a lot of money for their promoters and to evaluate their claims carefully. If she has to buy special foods, warn her that she'll probably regain weight she's lost when she goes back to eating regular food.
  • Provide follow-up care to monitor her progress and to encourage her to continue making healthy choices.
Back to Top | Article Outline

Is your patient overweight?

Considered the best way to determine obesity, the body mass index (BMI) is a ratio of weight in kilograms to height in meters squared. So, someone who's 65 inches tall and weighs 150 pounds has a BMI of 25.8 kg/m2. According to the American Heart Association, someone with a BMI between 18.5 and 24.9 kg/m2 is at a healthy weight. Someone with a BMI between 25 and 29.9 kg/m2 is overweight, and someone with a BMI of 30 kg/m2 or more is obese.

Another way to determine obesity is to measure the patient's waist. Women with a waist larger than 35 inches and men with a waist larger than 40 inches have central obesity.

Back to Top | Article Outline

How to spot a fad diet

Any of the following red flags signals bad nutritional advice:

  • recommendations that promise fast weight loss (more than 2 pounds per week)
  • claims that sound too good to be true, such as exercise isn't needed
  • dramatic statements that are refuted by reputable scientific research or organizations
  • recommendations based on a single study, studies published without peer review, studies that ignore differences from other reputable sources, or simplistic conclusions drawn from a complex study
  • lists of “good” and “bad” foods
  • recommendations that help sell a product.

June Daniels is a staff nurse at St. Vincent's Medical Center in Jacksonville, Fla.

Back to Top | Article Outline


American Dietetic Association

“Evaluate the Latest Diets,” WebMD

Food and Nutrition Information Center at the National Agricultural Library

“Quick-Weight-Loss or Fad Diets,” American Heart Association

Last accessed on November 1, 2004.

© 2004 Lippincott Williams & Wilkins, Inc.