Low-Carb Ketogenic Diet: Friend or Foe?

The first law of thermodynamics describes one of the most important principles related to biological work. The basic tenet states that energy cannot be created or destroyed but, instead, transformed from one form to another. That human beings obeyed the first law of thermodynamics was demonstrated by Drs. Atwater and Benedict in 1903 and has been continually reaffirmed since then. In accord with the first law of thermodynamics, the energy equation dictates that body mass remains constant when caloric intake equals caloric expenditure.

Any chronic caloric imbalance on the energy output or input side of the equation changes body mass. Three factors can unbalance the energy balance equation to produce weight loss: 1) reduce caloric intake below daily energy requirement; 2) maintain normal caloric intake and increase energy expenditure through additional physical activity above daily energy requirement; and 3) decrease daily caloric intake and increase daily energy expenditure.

Year after year, "new and improved" diets appear on bookstore shelves and circulate among friends. No matter what their names are, most fad diets espouse essentially the same low-carbohydrate diet. If low-carbohydrate diets were as successful as some people claim, consumers who tried them would lose lots of weight and our obesity problems would be solved. Obviously, this is not the case. Similarly, if low-carbohydrate diets were as worthless as others claim, consumers would eventually stop pursuing them. Clearly, this is not happening either. This article examines some of the science behind low-carbohydrate ketogenic diets.

Basic Facts About Ketogenesis

The major function of adipose tissue (fat tissue) is storage of the triglycerides (neutral fat) until they are needed to provide energy elsewhere in the body. The first stage in using triglycerides for energy is hydrolysis of the triglycerides into fatty acids and glycerol. Then, both the fatty acids and the glycerol are transported in the blood to the active tissues, where they will be oxidized (burned) for energy. Almost all cells, with some degree of exception for brain tissue, can use fatty acids almost interchangeably with glucose for energy.

Under metabolic conditions associated with a high rate of fatty acid oxidation (e.g., low-carbohydrate diet), the liver produces considerable quantities of acetoacetate, b-hydroxybutyrate and acetone. These three substances are collectively known as ketone bodies (also called [incorrectly] ketones). Ketosis does not occur unless there is an increase in the level of circulating free fatty acids that arise from lipolysis of triglycerides in adipose tissue. Free fatty acids are precursors of ketone bodies in the liver. The liver, in both fed and fasting conditions, extracts about 30 percent of free fatty acids passing through it, so that at high concentrations, the flux passing into the liver is substantial. Therefore, the factors regulating mobilization of free fatty acids from adipose tissue are important in controlling ketogenesis (production of ketone bodies).

When carbohydrates are not used for energy, almost all the energy of the body must come from metabolism of fats. Lack of availability of carbohydrates automatically increases the rate of removal of fatty acids from adipose tissue. In addition, several hormonal factors, such as increased secretion of glucocorticoids by the adrenal cortex, increased secretion of glucagon by the pancreas, and decreased secretion of insulin by the pancreas, further enhance the removal of fatty acids from the fat tissue. As a result, tremendous quantities of fatty acids become available 1) to the peripheral tissue cells to be used for energy and 2) to the liver cells, where much of the fatty acid is converted to ketone bodies. The ketone bodies pour out of the liver to be carried to the cells. The acetone that's formed during ketosis is a volatile substance, some of which is blown off in small quantities in the expired air of the lungs, often giving the breath an acetone smell. This smell is frequently used as a diagnostic criterion of ketosis.

Is the Low-Carb Diet a Friend?

According to Drs. Jeff Volek and Eric Westman, there is a lack of scientific evidence for the criticisms commonly made against low-carbohydrate diets, especially regarding metabolic mechanisms involved.²  Quite to the contrary, they feel there's a significant amount of scientific and anecdotal data demonstrating favorable metabolic responses to very-low-carbohydrate (ketogenic) diets (Table 1). Their recent review paper published in the Cleveland Clinic Journal of Medicine included the following key points:²

1. Most studies have found that people lose more weight on very-low-carbohydrate diets than on standard weight-loss diets.
2. Mechanism of weight loss on these diets may go beyond water loss and include suppression of appetite, increase in metabolic rate, decrease in metabolic efficiency, and shunting of nutrients away from fat storage.
3. Weight loss is usually associated with small to moderate reductions in lean tissue, but low-energy, very-low-carbohydrate diets have a protein-sparing effect compared with low-fat diets.
4. These diets may also have favorable effects on specific risk factors for cardiovascular disease.

Several short-term (under 12 weeks) trials have compared the effects of low-carbohydrate and high-carbohydrate diets on weight loss when energy intake was kept constant.¹⁰  These studies suggest that despite equal energy intakes, initial weight loss during the first four weeks may be greater with a low-carbohydrate diet than with a high-carbohydrate because a low-carbohydrate diet induces a greater loss of water; however, weight loss between six and 12 weeks was the same with either diet.¹⁰ 

Many currently popular low-carb diets (e.g., Atkins Diet) restrict carbohydrate intake, but allow unlimited intake of fat and protein. Some potentially valid explanations for promotion of weight loss by low-carb diets, despite unlimited fat and protein intake, include 1) initial diuresis (urine excretion) associated with ketone and nitrogen excretion; 2) losses of up to 100 calories per day in urinary ketones; and 3) most important, decreased energy intake, which may be related to ketosis, diet monotony, or other unknown mechanisms.¹⁰

Although it has been suggested that the high-fat and high-protein intakes associated with such diets may cause dehydration, electrolyte imbalance, hyperuricemia, calciuria, kidney stones, glycogen depletion with easy fatigue and hyperlipidemia, potential adverse effects of long-term ingestion of such diets have not been carefully investigated. No serious side effects were reported in a six-month trial involving 41 subjects receiving the Atkins diet.¹¹ These subjects, in fact, showed a 43 percent decrease in plasma triglycerides, an 18 percent increase in plasma HDL-cholesterol ("good cholesterol"), and a seven percent decrease in plasma LDL-cholesterol ("bad cholesterol").

However, the safety and efficacy of low-carbohydrate diets need to evaluated in long-term studies using a randomized, controlled trial.¹⁰

Catabolism of proteins is reduced by ketone bodies, which probably explains the preservation of lean tissue observed during very-low-carbohydrate diets. For example, Dr. Volek and co-workers examined the effects of a six-week carbohydrate-restricted diet on total and regional body composition and the relationships with fasting hormones.⁹  Twelve healthy normal-weight men switched from their habitual diet (48 percent carbohydrate) to a carbohydrate-restricted diet (eight percent carbohydrate) for six weeks and eight men served as controls, consuming their normal diets. Subjects were encouraged to consume adequate dietary energy to maintain body mass during intervention.

Fat mass was significantly decreased (-3.4 kilograms [kg]) and lean body mass significantly increased (+1.1 kg) at week six. However, there were no significant changes in composition in the control group. Authors concluded that a carbohydrate-restricted diet resulted in a significant reduction in fat mass and a concomitant increase in lean body mass in normal-weight men. They hypothesized that elevated b-hydroxybutyrate concentrations may have played a minor role in preventing catabolism of lean tissue, but other anabolic hormones were likely involved (e.g., growth hormone).

Is the Low-Carb Diet a Foe?

According to Dr. George Blackburn at Beth Israel Deaconess Medical Center, lack of data on the long-term safety and effectiveness of low-carbohydrate diets makes their medically unsupervised use very troubling, especially by those who may have a preclinical or "silent" condition or illness.³ For example, Dr. Reddy and colleagues recently found that very-low-carb diets delivered a marked acid load to the kidneys that increased the risk for kidney stone formation and the potential for bone loss contributing to osteoporosis.⁴

As pointed out by Dr. Blackburn, a key point about low-carbohydrate diets for weight loss is that the optimal weight loss diet is not necessarily the same as the optimal weight maintenance diet that promotes health and long life.³  Scientific studies that focus on foods eaten daily by people who are not on weight loss diets provide considerable evidence that diets low in saturated fats and high in fruits, vegetables and complex (low glycemic index) carbohydrates are safe and effective for maintaining weight and health.^5,6,7

Proponents of low-carbohydrate diets often blame the currently recommended high-carbohydrate/low-fat diet for our obesity problems. They claim the incidence of obesity is rising because we are eating less fat. True, the incidence of obesity has risen dramatically over the past two decades. True, our intake of fat has dropped from 36 to 34 percent of daily energy intake.⁸ However, the percentage declined only because average energy intake increased by 200 calories a day. Actual fat intake increased by four grams a day.⁸ Furthermore, fewer than half of us engage in regular physical activity.

Without vegetables, fruits and whole grain, low-carbohydrate diets lack not only carbohydrate, but fiber, vitamins, minerals and phytochemicals- all dietary factors protective against disease. To help shore up some of these inadequacies, low-carb diets often recommend a daily supplement. However, foods offer many more health benefits than any supplement can provide. Quite simply, if the diet is inadequate, it needs to be improved, not supplemented. It's my view that low-carbohydrate diets do not support optimal health over time.

            Guidelines for the Dieting Bodybuilder

• In my opinion, energy restriction is best achieved with a low-fat diet and a moderate carbohydrate intake. Protein intake should be about 1.5-2.5 grams/kilogram body weight. The upper level of protein is recommended if energy restriction is substantial, as this may assist with the maintenance of lean body mass and promote satiety.
• Set a realistic rate of weight loss (i.e., 0.5 to 1.0 kilogram [about one to two pounds] per week), including both short- and long-term goals.
• Keeping a food record for a defined period (e.g., a week) is a useful task that allows you to appreciate exactly what you are eating.
• A moderate energy restriction of 500 to 1,000 kilocalories per day is appropriate to produce a reasonable loss of body fat, but still ensure adequate nutrient intake.
• The meal plan for weight loss should not rely on skipping meals or enduring long periods without food intake. Rather, food intake should be spread over the day, particularly to allow for efficient refueling before and after training sessions and to avoid hunger (which generally precipitates overeating).
• Meals and snacks can be made more "filling" with several strategies: Low glycemic index carbohydrate choices (legumes, oatmeal, etc.) are considered to have a higher satiety value than high glycemic index choices (potatoes, white bread, etc.). Combine protein with carbohydrate-rich meals to produce greater satiety than in carbohydrate-rich foods alone. Also, add low-energy-density vegetables and fruits to meals to increase the volume of food you eat.
• Consider a broad-range, low-dose vitamin-mineral supplement if you will be restricting energy intake for prolonged periods.
• A myth that's circulating contends that in order to burn fat, you must exercise at a lower percentage of your maximal oxygen uptake (VO_2max). This is certainly not the case. It is true that the percentage of energy obtained from fat is greater at lower exercise intensities (e.g., 50 percent VO_2max) than at higher exercise intensities (e.g., 70 percent VO_2max). At the higher energy intensity, you will derive a lower percentage of your energy output from fat, but the total energy expenditure will be greater, and you will still burn about the same amount of fat calories as you would by exercising at the lower intensity, provided you are exercising for the same amount of time. If you want to burn calories to lose body fat, your objective should be to burn the greatest total calories possible within the time frame you have to exercise.
• Exercise, particularly intense exercise, may be used to curb appetite on a short-term basis at an appropriate time. If you exercise before a meal, your food intake may be reduced considerably. Try it and see if it works for you. If you have the facilities available, a good half-hour exercise may be an effective substitute for a large lunch.
• Ephedrine and caffeine have been- and still are- used for weight reduction in obese patients. Ephedrine at a dose of 150 milligrams daily can produce weight loss, but best results are produced with the ephedrine-caffeine combination. The doses used in studies were 20 milligrams ephedrine and 200 milligrams caffeine daily, and these were effective when combined with reduced energy intake. However, caffeine alone does not seem to be effective. The side effects of ephedrine are tremor and nervousness, elevated blood pressure and increased heart rate. While useful for those with asthma, ephedrine should not be used by those with diabetes, hypertension or hyperthyroidism. Nor should ephedrine-based products be used by patients taking Prozacä and related antidepressants. The International Olympic Committee (IOC) prohibits use of ephedrine during competition. Also, taking an ephedrine/ephedra-based product and applying for a new job is not a good idea. The structure of the ephedrine molecule bears a very strong resemblance to that of all of the other amphetamines. Most urine screening tests will also detect ephedrine.

References

1. Guyton AC Hall JE (2000) Textbook of Medical Physiology. Philadelphia: W. B. Saunders.
2. Volek JS, Westman EC (2002) Very-low-carbohydrate weight-loss diets revised. Cleve Clin J Med, 69:849-862.
3. Blackburn GL (2002) Making good decisions about diet: Weight loss is not weight maintenance. Cleve Clin J Med, 69:864-866.
4. Reddy ST, Wang CY, Sakhaee K et al. (2002) Effect of low-carbohydrate high-protein diet on acid-base balance, stone-forming propensity, and calcium metabolism. Am J Kidney Dis, 40:265-274.
5. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults: the evidence report. Washington, DC: National Institutes of Health, 1998. Available: http://nhlbi.nih.gov/guidelines/obesity/e_txtbk/index.htm
6. Anderson JW, Konz EC, Jenkins DJ (2000) Health advantages and disadvantages of weight-reducing diets. Am J Clin Nutr, 19:578-590.
7. Fletcher-Mors M, Ditschuneit H, Johnson T et al. (2000) Metabolic and weight loss effects of long-term dietary interventions in obese patients. Four-year results. Obes Res, 8:399-402.
8. Whitney EN, Rolfes SR (2002) Understanding Nutrition. Belmont, CA: Wadsworth/Thomson Learning.
9. Volek JS, Sharman MJ, Love DM et al. (2002) Body composition and hormonal responses to a carbohydrate-restricted diet. Metabolism, 51:864-870.
10. Klein S, Romijn JA (2003) Obesity. In: Larsen PR, Kronenberg HM, Melmed S, Polonsky KS, eds. Williams Textbook of Endocrinology. Philadelphia: Saunders, pp. 1619-1641.
11. Westman EC, Yancy WS, Edman JS et al. (2000) Effects of a very-low-carbohydrate program on body weight: a pilot study (abstract). Obes Res, 8:(Suppl):73S.
12. Williams MH (2001) Nutrition for Health, Fitness and Sport. New York: WCB/McGraw-Hill.
13. O´Connor H, Sullivan T, Caterson I (2000) Weight loss and the athlete. In: Burke L, Deakin V, eds. Clinical Sports Nutrition. Australia: McGraw-Hill Australia, pp. 146-184.
14. Karch SB (1999) The Consumer´s Guide to Herbal Medicine. Hauppage, NY: Advanced Research Press