Diets come and diets go. Sometimes it seems the only thing that sticks around is the fat. Most of America bases diet choice on the popular media, which is constantly seeking the "next revolution" in dieting to grab the attention of shoppers standing in checkout lines, usually next to the candy and snacks.

The seasonal change in "ultimate dieting tips" is bewildering enough without further confusion created by the arguments among scientific experts or the yo-yo appearance of celebrity endorsers. For many years, the most commonly practiced diets focused on cutting out dietary fat, often eliminating many protein sources as well. Based in part upon the food pyramid, carbohydrates were the mainstay of the diets. Success with these low-fat, high-carbohydrate diets were variable, with some losing fat, others actually gaining.

Forbidden Fruit
Recently, another strategy in dieting has come back into vogue.1,2 Completely contrary to the recommendations of the diet plans of ‘70s and ‘80s, many diet plans now promote avoiding carbohydrates almost entirely. These diets are collectively referred to as "ketogenic diets." While there are some differences in the many plans (Atkins, Protein Power, Sugar Busters, Greenwich, etc.), they are all based on restricting carbohydrate intake. Instead, food selection is made from choices high in protein and fat.

A great deal of attention has been focused on the ketogenic diets, in part due to the reported success of followers of the Atkins diet and the media exposure of its namesake, Dr. Robert Atkins. This attention has proven to be a double-edged sword, as many scientists and agencies are now disputing the effectiveness of the diet and questioning its long-term safety.3

Ketogenic diets work in some ways common to all diets and others unique to the low-carbohydrate approach. As with all diets, a caloric deficit must be achieved in order to promote a loss of body fat. There is a popular misconception that ketogenic diets allow you to eat all you want of the foods you love. This may seem true since many foods that would be taboo in traditional low-fat diets form the foundation of ketogenic diets, such as red meat, eggs, dairy products and seafood. However, an excess of calories, whether from carbohydrates, protein or fat, will lead to weight gain.

The intent of a ketogenic diet is to create a state known as "starvation ketosis"4,5 by depleting the body of both dietary sugars and stored sugars, such as glycogen. Normally, such a strategy would cause severe muscle wasting within a matter of days to weeks. However, by providing a near maintenance level of calories and a steady influx of protein, lean mass may be preserved. Indeed, many bodybuilders claim to sustain and even increase muscle size and strength while on a ketogenic diet.

Individuals considering losing weight by means of a ketogenic diet should be fully aware of how such diets work and some of the associated risks. Ketogenic diets are very strict in terms of food choices. Despite having the liberty to choose from previously forbidden foods, such as steak, hamburger and omelets, the restrictions are against all produce, juices, soda, breads, pasta and rice. Indeed, the apple once again becomes "forbidden fruit."

Breath Test?
Ketogenic diets work by creating starvation ketosis, in which the body is forced to burn stored fat for calories when sugar, from both the diet and stored sugars such as glycogen, are not available. While fat is calorie dense, meaning it provides more calories than a comparable amount of sugar, fat is not handled as efficiently by the body. Incomplete fat metabolism (burning) leads to the production of byproducts called ketones- small molecules that can be used for energy in place of glucose, or that may be excreted through the urine or even by breathing.

Many Type I diabetics, who may suffer from a severe form of ketosis called ketoacidosis, develop "fruity" smelling breath due to excess acetone production.6 Acetone is a ketone produced during ketosis and is chemically identical to the solvent acetone. Many people on a ketogenic diet may receive comments from others that their breath is different, or even unpleasant. While not socially favorable, this is a positive sign that the diet is working to create a ketogenic state, with near maximal fat burning.   

Achieving a ketogenic state is very difficult and remaining in ketosis is next to impossible. Ketones are only produced when calorie burning is almost exclusively due to fat metabolism. The presence of even a small amount of carbohydrates in the daily diet can greatly reduce ketone production.7  Many of the ketogenic diets restrict carbohydrate intake to 40 grams or fewer per day.3 In conversation, Body Opus guru Dan Duchaine mentioned that even the regular chewing of "sugar-free gum" could provide enough sugar (through sugar alcohols) to prevent reaching ketosis.8

Most people are unaware of the many sources of "hidden" carbohydrates, including medication- both prescription and over-the-counter, supplements, "sugar free" diet products, sauces, etc.9  Even small amounts of sugar can have an "anti-ketotic" effect.5 This may represent a function of evolutionary adaptation since stored body fat may have been essential to surviving periods of famine, making it vital to preserve body fat whenever food was available. There are reported cases of political and religious zealots surviving up to 60 days without food before perishing.5

The reduction in stored sugar within the body is likely the primary method by which early weight loss occurs in ketogenic diets. Glycogen, the stored sugar form, is responsible for increasing water retention in the cells. By decreasing glycogen stores to a minimum, there's an associated loss of water weight, accounting for much of weight lost in the first week.3 The loss of water from within the cell also accounts for the "flat" look that plagues many bodybuilders using ketogenic diets.

While ketones are formed and burned for fuel in nearly every cell of the body, the ketones found in the blood come almost exclusively from the liver.6  The liver is capable of breaking down the ketones to a form that can be transported through the blood and delivered to other vital organs, such as the heart and brain. The ketones provided by the liver can be created from stored body fat or from fat obtained in the diet. Again, it is important, even when using ketogenic dieting techniques, to maintain calorie control at or slightly below maintenance levels.

The Protein Factor
The other macronutrient allowed in ketogenic dieting is protein. Studies have shown that in ketogenic states, there is typically a great deal of muscle wasting, as most diets are limited in providing sufficient quantities of the essential amino acids, thereby limiting new protein production.5  Additionally, there is a greater loss of muscle as the proteins are broken down to amino acids and burned for calories. The branched chain amino acids (BCAA), present in high concentrations in the muscle, are particularly vulnerable, as they can be converted into ketones and used for fuel, just like the ketones from fat.

Research has shown that the loss of lean mass and muscle can be reduced or prevented if a sufficient amount of protein is included in the diet.10  While no hard and fast rules have been established for protein content of ketogenic diets, many of the established diets are promoting high levels of protein, often providing as much as 50 percent of daily calories or more. It may seem that in the extremely catabolic state created by the ketogenic diets, that the maximum amount of protein tolerated would be best. However, consuming too much protein may actually inhibit ketosis and prevent weight loss.

Proteins are long chains of amino acids. There are over 20 different amino acids in the diet. As stated earlier, some of the amino acids are used to rebuild proteins, preventing the loss of muscle and lean mass. However, certain amino acids can also be used to create sugar, and an excess of amino acids may provide enough sugar to block the production of ketones.

In addition to being capable of becoming sugars, amino acids can signal insulin release if consumed in large quantities.5 Reducing insulin is considered to be an important feature of ketogenic diets. Insulin is a very potent hormone that can prevent the release of stored fat from the fat cells.11 If insulin levels are kept low, it is felt that fat release occurs uninhibited, promoting fat loss.

Ketones do not promote fat burning, but are an important component of the ketogenic diets. The presence of ketones is evidence that fat burning is proceeding at a maximal rate. The ketones also provide the benefit of suppressing the appetite,12 making it easier to control hunger and preventing any binge eating. Lastly, and for some, most importantly, ketones are able to reduce the loss of muscle experienced during dieting.

As mentioned earlier, the BCAAs, found in high concentration in the contractile protein of muscle, are broken down rapidly during low-sugar states. The BCAAs are not converted into sugar as are many of the amino acids; rather they are converted into ketones. It has been discovered that ketones from fat burning can be taken in by the muscle and inhibit muscle breakdown.5,13 This explains the reports by some bodybuilders that ketogenic diets allow for greater strength and muscle retention as opposed to other low-calorie diets.

Facing Challenges
While ketogenic diets have a sound scientific argument for being the best fat reduction diet scheme, there are some valid arguments against recommending many of the ketogenic diets.3  Ketogenic diets restrict fruits, vegetables and grains, which are the source of most of the vitamins, minerals and other phytonutrients that are required daily for health. A strict ketogenic diet could place one at risk for vitamin deficiency states, such as scurvy, unless proper vitamin supplementation is provided.14 It's very important that anyone on a ketogenic diet use a high-quality vitamin and mineral supplement. Another drawback to ketogenic diets is a lack of fiber, increasing the likelihood of stool problems, such as constipation or hemorrhoids. A fiber supplement should be used, such as psyllium powder.15

High protein diets have been associated with kidney stone formation.16,17 Individuals with a family history of kidney stones or gout should discuss the decision with a qualified physician. It's important to drink plenty of water daily when using a ketogenic diet to avoid a build-up of certain waste products.
Perhaps the greatest challenge to ketogenic diets is the dependence upon dietary fat and the increased consumption of saturated fats and cholesterol. While many studies have found negative changes in blood lipids, others have documented positive changes. Recently, the American Heart Association (AHA) has released a general recommendation against most ketogenic diets.3 The concern of the AHA is that the avoidance of antioxidant- rich foods, low fiber content and higher intake of saturated fat would increase the risk of vascular disease, such as heart attacks and strokes. Some of the ketogenic diets address this issue by replacing mono- and polyunsaturated fats, such as olive oil and flax seed oil, in place of animal fats from meats, dairy and egg products.18,19 As with any diet, people with health concerns or questions should discuss the issue with a physician.4

    Wrapping Up
In summary, ketogenic diets can be an effective means of weight control and fat reduction.20 The diets allow for foods not normally considered "diet food," but require strict adherence to food choices to avoid any significant carbohydrate sources. Attention still must be paid to keep daily calories at or below maintenance levels. The initial weight loss is quick, but is typically due to water loss. However, the weight loss can continue and many people report losing two or more pounds per week.

Dieters should consider supplementing with a potent vitamin and mineral formula, as well as a fiber product. Increasing the intake of protein may prevent the loss of muscle and lean mass commonly seen with ketogenic diets. Water should be consumed in abundance to avoid the build-up of waste products, particularly for those individuals consuming large quantities of protein. Concerns have been raised over relying upon a ketogenic diet for long periods, due to the high content of saturated fats, though substituting fish and plant-based oils for animal fats should reduce the risk of health concerns.  

By definition, ketogenic diets create the maximal fat burning possible and may represent the most effective means of weight loss and fat reduction. If followed strictly, with appropriate supplementation and guidance, most people should be able to experience success.

References  
1.    Banting, W. Letter on Corpulence, 4th Edition. 1869, Harrison, London.
2.    Atkins, RC. Dr. Atkins' New Diet Revolution. 1996, Avon Books, New York.
3.    St. Jeor ST, Howard BV, et al. Dietary protein and weight reduction. Circulation 2001;104(15):1869
4.    Sankar R, Sotero de Menezes M. Metabolic and endocrine aspects of the ketogenic diet. Epilepsy Res 1999 Dec;37(3):191-201.
5.    Ganong WF. Review of Medical Physiology, 19th edition. 1999 Appleton & Lange, New York.
6.    Laffel L. Ketone bodies: a review of physiology, pathophysiology and application of monitoring to diabetes. Diabetes Metab Res Rev 1999 Nov-Dec;15(6):412-26.
7.    Freeman JM. 10 Questions about the ketogenic diet. Neurologist 2000 May;6(3):197-201.
8.    Personal communication with Dan Duchaine.
9.    McGhee B, Katyal N. Avoid unnecessary drug-related carbohydrates for patients consuming the ketogenic diet. J Am Diet Assoc 2001 Jan;101(1):87-101.
10.    Willi SM, Oexmann MJ, et al. The effects of a high-protein, low-fat, ketogenic diet on adolescents with morbid obesity: body composition, blood chemistries and sleep abnormalities. Pediatrics 1998 Jan;101(1 Pt 1):61-7.
11.    Ferrannini E, Galvan AQ, et al. Insulin: new roles for an ancient hormone. Eur J Clin Invest 1999 Oct;29(10):842-52.
12.    Scharrer E. Control of food intake by fatty acid oxidation and ketogenesis. Nutrition 1999;15(9):704-14.
13.    Morgan WD, Ryde SJ, et al. Changes in total body nitrogen during weight reduction by very-low-calorie diets. Am J Clin Nutr 1992 Jul;56(1 Suppl 1):262S-264S.
14.    Tallian KB, Nahata MC, et al. Role of the ketogenic diet in children with intractable seizures. 1998 Mar;32(3):349-61.
15.    McRorie JW, Daggy BP, et al. Psyllium is superior to docusate sodium for treatment of chronic constipation. Aliment Pharmacol Ther 1998 May;12(5):491-7.
16.    Furth SL, Casey JC, et al. Risk factors for urolithiasis in children on the ketogenic diet. Pediatr Nephrol 2000 Nov;15(1-2):125-8.
17.    Kielb S, Koo HP, et al. Nephrolithiasis associated with the ketogenic diet. J Urol 2000 Aug;164(2):464-6.
18.    Lairon D. Dietary fatty acids and arteriosclerosis. Biomed Pharmacother 1997;51(8):333-6.
19.    Volek JS, Gomez AL, et al. Fasting lipoprotein and postprandial triacylglycerol responses to a low-carbohydrate diet supplemented with n-3 fatty acids.  J Am Coll Nutr 2000 Jun;19(3):383-91.
20.    Wing RR, Vazquez JA, et al. Cognitive effects of ketogenic weight-reducing diets. Int J Obes Relat Metab Disord 1995 Nov;19(11):811-6.