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High Protein vs Low Carbohydrate Diets
Fact & Fantasy


Another Opinion

Cedric X. Bryant, Ph.D., FACSM, James A. Peterson, Ph.D, FACSM, and Jason M. Conviser. Ph.D., FACSM

“National surveys reveal that approximately 20 million adults in the U.S. are dieting to lose weight, and another 20 million think they should be. People are barraged with a seemingly never-ending abundance of nutrition and weight control information as new research, diets and exercise programs emerge. In fact, an estimated $30 billion is spent annually on diet books, products and services. Unfortunately, most of the information published is complicated and even fraudulent. The resulting chaos is leading many people to make serious, even life-threatening mistakes in pursuit of their ultimate goal of meaningful, permanent weight loss. “Sugar Busters!,” “The Zone,” “Dr. Atkins’ New Diet Revolution,” “Protein Power,” and “The Carbohydrate Addicts Diet” are some of the latest fad diets that have become popular – and controversial. These books all feature diets that allegedly hold the “key to lifetime thinness.” The common theme running through these books is that people should eat a high protein diet, instead of the high carbohydrate diet recommended by most health and fitness professionals.

The basic claims of these authors is that carbohydrates make people fat, and that insulin causes obesity. These diets focus on blood sugar levels and blame carbohydrates for causing a sudden rise in blood sugar. During metabolism, as blood sugar levels rise, insulin is released to send sugar to the brain and muscles to be burned for energy, while the excess is stored as fat. The theory is that if individuals limit their intake of carbohydrate, the rapid rise in blood sugar is avoided and less sugar will be stored as fat. These diets also claim that, by eating a high protein, higher-fat diet, the body will preferentially metabolize fat instead of carbohydrate for energy.

No sound scientific evidence exists to support these author’s claims. And unfortunately, these ill-founded claims can have a significant influence on an individual’s behavior. This article addresses the validity of several of the popularly held myths and misconceptions regarding high-protein, low-carbohydrate diets and their impact on weight control.

Myth #1: Carbohydrates and insulin cause weight gain.

Insulin isn’t a harmful hormone. It is essential for the transport of glucose (sugar) from the bloodstream to the body’s cells (e.g. muscle and adipose) where it fuels all activities. What determines weight loss is not carbohydrates and insulin, but an individual’s level of caloric consumption. Obtaining a high percentage of calories from
carbohydrates does not make an individual fat, because weight gain is a function of caloric balance. If the individual consumes more calories than they burn, they will gain weight.

Individuals must closely monitor their levels of caloric consumption to effectively channel their weight-control efforts. Unfortunately, when encouraged to eat more carbohydrates and less fat, some individuals misinterpret the full intent of the message. They think it gives them a license to eat as much high-carbohydrate food as they want, as long as the food is fat-free. As a result, they consume far too many low-fat sweets and extra large portions of starches. Consequently, they have difficulty losing weight and erroneously blame carbohydrates.

Trimming fat calories reduces total caloric consumption more than cutting back on foods high in carbohydrates, because fat provides more than twice the calories by weight (9 kcal/gram vs 4 kcal/gram). In addition, the body converts dietary fat into body fat more efficiently than it converts dietary carbohydrate into body fat. For example, if a person consumes 100 extra calories from dietary fat (e.g. one tablespoon of butter), only 3 calories are used by the body to transform the butter into body fat. One hundred extra calories of carbohydrate, on the other hand, require 23 calories to make the transformation. In other words, a given caloric quantity of excess dietary fat is more fattening than a comparable quantity of excess carbohydrate. However, an individual who reduces the amount of calories consumed as fat, but adds them back in the form of carbohydrate calories is not going to lose weight.

The basic law of thermodynamics cannot be defied. When individuals eat more food than they need, whether the extra calories come from fat, protein or carbohydrate, they will gain weight.

Myth #2: High-protein, low carbohydrate diets are recommended for the larger number of individuals who are insulin resistant

Approximately 10 to 25 percent of people in the U.S. suffer from insulin resistance. These individuals show a greater likelihood for having hypertension (high blood pressure), hypertriglyceridemia ( elevated levels of body fat) and reduced levels of high-density lipoprotein (HDL), all of which represent significant risk factors for heart disease. The muscle, liver and fat cells of these individuals have less responsiveness to the action of insulin.

When insulin resistant people consume carbohydrates, the pancreas compensates by dramatically increasing insulin secretion to maintain normal blood glucose levels. According to the various self-proclaimed nutrition experts, this hyper-secretion of insulin causes carbohydrates to be stored as fat. It is for this reason that insulin-resistant people are best helped by consuming high-protein, low-carbohydrate diets.

No reputable scientific evidence exists, however, to support the notion that insulin resistance or a high blood insulin level make individuals fat. Consuming a high-carbohydrate diet does not cause insulin resistance. Furthermore, high insulin levels are not the cause of excess body fat in individuals with insulin resistance. A sedentary lifestyle and midlife weight gain are much more significant factors. People with type 2 diabetes or “Metabolic Syndrome X” experience tremendous health benefits by increasing their physical activity levels and losing modest amounts of weight. In fact, reducing excess weight and increasing physical activity are more important factors than is the dietary percentage of protein and carbohydrates.

Weight reduction and physical activity both improve insulin sensitivity, and enhanced sensitivity results in lower blood insulin levels. Weight loss allows the peripheral cells to properly respond to insulin so that less insulin is required. Exercising regularly causes insulin to more easily bind to muscle cell receptors and to promote a more effective uptake of glucose. Weight loss and exercise also produce additional significant health benefits (reduced risk of hypertension, increased HDL levels, lowered triglyceride levels, etc.).

Myth #3: High-Protein, low-carbohydrate diets cause metabolically induced, rapid weight loss.

One of the reasons individuals lose weight on high-protein, low-carbohydrate diets is because of severe caloric restriction, not because of some effect related to serum insulin levels. Unfortunately, many individuals also lose something else: their performance capacity and general well-being. Individuals need to consume sufficient amounts of calories and carbohydrates to maintain their muscle glycogen stores, which are the primary fuel source for working muscles. Another reason for the large rapid weight loss often associated with high-protein diets is due to significant water loss, not fat reduction. Such a loss occurs because protein metabolism requires extra water for utilization and excretion (i.e. elimination) of its byproducts.

Myth #4: High-carbohydrate diets impair exercise performance.

Despite assertions to the contrary by the authors of carbohydrate-bashing books, a diet high in carbohydrates is essential for optimal physical performance. Carbohydrates are an important means of replenishing glycogen stores. Glycogen is the muscle’s preferred source of fuel during aerobic exercise, because it is more efficiently converted to energy. The availability of glycogen has been shown to influence the amount of exercise individual’s can accomplish before fatigue occurs.

The supply of muscle glycogen during vigorous exercise can last from 60 to 90 minutes, depending on how much of this energy was stored in the muscles prior to the onset of exercise. The amount of glycogen stored depends upon the level of daily
carbohydrates and caloric replenishment, and on the individual’s level of fitness. As a general rule, the better trained people are, the more glycogen they can store. A non-exercising individual who eats a proper diet and participates in normal daily activities will not experience a depletion of muscle glycogen during a typical day, even though muscle glycogen is constantly being used. However, engaging in normal daily activities, in addition to prolonged or intense exercise, will result in the greater use of glycogen for fuel, thereby depleting glycogen stores. Exercisers have termed this depletion as “hitting the wall” or “bonking,” because is correlates to fatigue and exhaustion.

Low or depleted muscle glycogen stores at the onset of aerobic exercise, or glycogen stores that become low or depleted during exercise, can cut an individual’s workout short due to premature fatigue and exhaustion caused by a lack of sufficient fuel. Low or depleted muscle glycogen stores can limit the intensity at which an individual exercises, or can result in a tired and listless feeling for the remainder of the day, or until the muscle glycogen stores are replenished. No one who exercises wants to experience the symptoms of low or depleted muscle glycogen stores, which can result in a compromised workout or influence the outcome of competition. Consequently, ensuring a sufficient intake of dietary carbohydrates should be of paramount concern to physically active individuals.

A low-calorie diet in disguise:

The popular high-protein, low-carbohydrate diets are simply low-calorie diets that restrict an individual’s level of carbohydrate consumption. In reality, low-calorie diets that limit carbohydrate intake can have serious nutrition and health consequences. They eliminate many food groups that provide essential nutrients, energy and fiber (e.g., breads, grains, cereals, fruits and vegetables). Furthermore, they do not teach or promote good nutritional habits. The dieter learns little about making wise food choices, or about making sound lifestyle changes that will help them to maintain their weight loss. In addition, these diets can cause dehydration that persists until the diet is over. Finally, low-calorie diets provide limited carbohydrates for glycogen replacement. As a result, a dieter quickly becomes glycogen depleted, making exercise difficult, especially when combined with dehydration. Ultimately, these factors will set any exercising dieter up for failure.


Author/speaker and an expert in ”Sports Performance Enhancement”. Jack Medina is available for speaking engagements, consultation and personal training of athletes in various sports, professional and amateur. Jack has written a new book, “The Winning Edge: Fueling & Training The Body For Peak Performance” with Dr. Roy Vartabedian, an internationally known New York Times Best Selling Author of the “Nutripoints” program for optimal nutrition. Both books are available online at www.jackmedina.com. Jack also has a monthly ezine (newsletter) available free which can be subscribed to on his website. All subscriber’s addresses will be confidential and not sold or given to any other organization or group.

This article contains copyrighted material. Copies of this article may be reprinted without permission of the author only when this bi-line is included with each copy. Jack can be reached at jack@jackmedina.com