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Very Low Carbohydrate Diets and Fat Loss: The Fat Truth fit woman exercising

by: Anssi Manninen, M.H.S.

Reproduced, with permission, from Muscular Development


Advances are made by answering questions. Discoveries are made by questioning answers.”
Bernard Haisch”

For decades, the United States Department of Agriculture (USDA) has taught us that a diet low in fat and high in starch (e.g.,USDA Food Pyramid) promotes fat loss and decreases the risk of chronic diseases. It should be noted, however, that there’s little, if any, scientific evidence supporting this notion. In fact, the current epidemic of obesity has been accompanied by a significant decrease in fat consumption and an increase in carbohydrate consumption. Thus, alternative dietary approaches are clearly needed, especially for fat loss.

Strength/power athletes and fitness models already know what science is now showing: when one wants to maximize fat loss while building muscle mass, a very low carbohydrate/high-protein diet is the way to go. Also, the purported adverse effects of such diets are greatly exaggerated, at least in the short-term. This article refutes the enduring myths regarding low carbohydrate diets; reviewing some studies examining the effects of such diets on body composition. This article also provides dietary guidelines for those who want to cut all the extra fat, while simultaneously increasing muscle mass.

Very Low Carbohydrate Diet-Related Urban Legends

Some well-meaning yet sadly misinformed nutritionists have claimed that additional weight loss on very low carbohydrate diets is entirely due to the loss of body water. However, the classic study by Dr. Rabast and co-workers demonstrated that alterations in the water and electrolyte balance observed during low-carbohydrate diets are reversible phenomena and should thus not be regarded as causal agents. Also, more recent studies measuring body composition by dual-energy X-ray absorptiometry have not found any indication of dehydration (an abnormal depletion of body fluids). So, the greater weight loss from a very low carbohydrate diets is largely attributable to fat loss.

Old school nutrition ‘experts’ have also proposed that a very low carbohydrate diet sets the stage for a significant loss of muscle mass, as the body recruits amino acids from muscle protein to maintain blood sugar (glucose) via gluconeogenesis (formation of glucose within the body from precursors other than carbohydrates). This assumption is clearly fallacious. It is true that animals share a metabolic deficiency, which gives rise to the almost total inability to convert fatty acids to glucose. Hence, the primary source for a substrate for gluconeogenesis is amino acids. However, when the rate of mobilization of fatty acids from fat tissue is accelerated (e.g., during a very low carbohydrate diet), the liver produces ketones. The liver cannot utilize ketones and thus, they flow from the liver to extra-hepatic tissues (e.g., brain, muscle) for use as a fuel. Simply stated, ketone body metabolism by the brain displaces glucose utilization and thus spares muscle mass. In other words, the brain derives energy from stored fat during a very low carbohydrate diet. Also, if the muscle is more than sufficiently supplied with other substrates for burning (such as fatty acids and ketone bodies, in this case), then the burning of muscle protein-derived amino acids is suppressed.

Dietary ketosis is a harmless physiological state caused by regulated and controlled production of ketones. Unfortunately, many health care professionals have confused dietary ketosis with diabetic ketoacidosis. All diabetic patients know that the detection in their urine of ketones is a danger signal indicating that their diabetes is poorly controlled. Indeed, in severely uncontrolled diabetes, if ketones are produced in massive supranormal quantities, they are associated with ketoacidosis. In this life-threatening complication of diabetes mellitus, ketones are produced rapidly, which overwhelm the body’s acid-base buffering system. However, a very low carbohydrate diet cannot lead to dangerous ketoacidosis in healthy subjects (without alcohol or drug abuse), because ketones have effects on insulin and glucogen secretions that contribute to the control of the rate of their own formation.

A Calorie is Still Not a Calorie

In 2002, USDA researchers published a review paper in the Journal of the American Dietetic Association, claiming that, “the results of several of the [low-carbohydrate] studies actually refute the contention that low-carbohydrate diets, in the absence of energy restriction, provide a metabolic advantage for weight loss”. They cite four studies supporting this proposition. As pointed out by my colleague Gary Taubes, however, these studies actually don’t support their position. Quite the contrary. One of the studies cited by the USDA authors followed 24 obese men and women; two weeks on their usual food intake, eight weeks on Atkins diet; and then again for two weeks on their usual diet. The abstract of this paper states, “The high-protein, low-carbohydrate dieting resulted in substantial weight loss, probably due to a combination of salt and water loss, as well as caloric restriction.” However, the full paper offers some interesting details. Average weight loss from the Atkins diet was about 0.9 kilograms (2 pounds) per week. The authors pointed out that they would have predicted only half of that to be from the apparent reduction in calorie intake, and that they could account for another quarter of a kilogram by taking into account water weight: but still fall nearly 0.2 kilograms short per week. So, the suggestion that this study refutes contention that low carbohydrate diets provide a metabolic advantage is simply ridiculous. Apparently, the USDA authors didn’t bother to read the full papers. Alternatively, it is possible that they simply wanted to get an article into print that appeared to support the USDA’s Food Pyramid. To look at the evidence and go away unconvinced is one thing. To not look at the evidence and be convinced against it nonetheless is another, but that’s certainly not science.

A number of well-controlled scientific studies have demonstrated that a very low carbohydrate diet promotes fat loss while maintaining or even increasing muscle mass. For example, Dr. Young and co-workers compared three diets containing the same amounts of calories (1,800 kcal/day) and protein (115 grams/day) but differing in carbohydrate content. After nine weeks on the 30-g, 60-g and 104-g carbohydrate diets, weight loss was 16.2, 12.8 and 11.9 kg and fat accounted for 95, 84, and 75% of the weight loss, respectively. So, the authors concluded,
“Weight loss, fat loss, and percent of weight loss as fat appeared to be inversely related to the level of carbohydrate in the isocaloric, isoprotein diets.” In layman’s terms, the more carbohydrates these test subjects consumed, the less body fat they lost. This study was published in the well-respected American Journal of Clinical in 1971, but was evidently ignored by obesity ‘authorities’ (don’t confuse me with the facts, a calorie is always a calorie).

Dr. Jeff Volek and colleagues investigated the effects of a six-week very low carbohydrate diet on body composition in healthy normal-weight men. 12 subjects switched from their habitual diet (48% carbohydrates) to a very low carbohydrate diet (8% carbohydrates) for six weeks and eight men served as controls, consuming their normal diet. Although subjects were encouraged to consume adequate dietary energy to maintain body mass during the intervention, the results revealed that fat mass was significantly decreased (-3.4 kg) and lean body mass significantly increased (+1.1 kg) at week six. There were no significant changes in
composition in the control group. The authors concluded that a very-low-carbohydrate diet resulted in a significant reduction in fat mass and an accompanying increase in lean body mass in normal-weight men. In other words, the entire loss in bodyweight was from body

Another well-controlled study by Dr. Volek and co-workers compared effects of isocaloric, energy restricted very low carbohydrate diet and low-fat/high-carbohydrate diets on weight loss and body composition in overweight/obese men and women. Despite significantly
greater calorie intake (1855 versus 1562 kcal/day), a group comparison revealed the distinct
advantage of a very low carbohydrate diet over a low-fat diet for weight loss/fat loss for men. In fact, five men showed more than 10 pounds difference in weight loss. The majority of women also responded more favorably to the very low carbohydrate, especially in terms of trunk fat loss. Furthermore, individual responses revealed that three men and four women who did the very low carbohydrate diet first, regained body mass and fat mass after the switch to the low-fat diet, whereas no subjects regained weight or fat mass after switching to the very low carbohydrate diet.

For a more detailed review, I suggest you read my recent scientific papers published in the Journal of the International Society of Sports Nutrition and Nutrition & Metabolism.* Once you have read them, you will also conclude that, when it comes to fat loss, a calorie is certainly not a calorie. In fact, it seems to me that calorie content may not be as predictive of fat loss as is reduced carbohydrate consumption. Similarly, a recent comprehensive meta-analysis (a statistical analysis of a large collection of similar studies) examined a total of 87 well-controlled studies and clearly showed that very low and low-carbohydrate diets promote fat loss, independent of calorie intake. This meta-analysis also showed that higher protein intake is associated with greater retention of muscle mass.

*Free full text papers are available at…

The Ultimate Nutritional Program for Short-Term Fat Loss

This program is targeted to those who wish to maximize short-term fat loss while maintaining or increasing muscle mass.

1. Follow a very low carbohydrate, high-protein, moderate-fat diet. The most important point is to keep carbohydrate intake very low. Also, make sure you take in adequate amounts of protein with every meal. You hardly need to limit fat intake during a very low carbohydrate diet. Avoid trans fats though. Choose only low-glycemic, high-fiber carbohydrate sources (vegetables, legumes, etc.). However, immediately after resistance exercise you can take in a small amount of high-glycemic carbohydrates with a fair amount of high quality protein (e.g., hydrolysed whey protein). Good protein sources include fish (healthy fats!), eggs, lean
meats, and carbohydrate-free protein powders.

2. The critical supplements are multivitamin-mineral complex, pure creatine monohydrate powder or carbohydrate-free creatine transport formula (e.g., ProSource SynthaTrex), and a well-designed fat loss-enhancing supplement (e.g., iSatori Lean System 7, EAS Thermo DynamX). Also suggested is branched-chain amino acid leucine to stimulate muscle protein synthesis. However, you certainly should not look to supplements to be a ‘magic bullet’ to make up for not paying adequate attention to your basic nutritional program.

3. Remember to drink lots of water and other calorie-free fluids. Also, it is very important to take in adequate amounts of sodium and potassium. A very low carbohydrate diet increases sodium excretion, and the excessive loss of sodium in the urine could reduce blood volume and cause secondary potassium wasting. If you decide to give this program a try, you may need to modify your resistance-training program. For example, it’s a good idea to focus on heavier weights for fewer reps (three to eight), because the energy is primarily derived from phosphocreatine stores. Phosphocreatine serves as the cell’s energy reservoir to provide rapid phosphate-bond energy to resynthesize ATP, a high-energy molecule serving as the ubiquitous energy currency of cells. This is a more rapid pathway than ATP regeneration in glycogen breakdown (glycogenolysis). Thus, phosphocreatine becomes important in maximum efforts lasting up to 10 seconds. Ingesting creatine monohydrate at the dosage of 20 to 30 grams per day for two weeks increases intramuscular concentrations of free creatine and phosphocreatine by up to 30 percent. Consequently, creatine is a very useful supplement to use during a very low carbohydrate diet.

This program is not for serious endurance athletes; they need more carbohydrates. Consult with your physician before starting this program if you have any medical condition or if you are taking any medication. Do not follow this program if you are pregnant or nursing.

Lifelong Health and Weight Control

Although a very low carbohydrate diet is a very effective short-term approach to fat loss, a moderate-carbohydrate diet is probably the most effective diet for lifelong health and weight control. Just make sure you stick with ‘good carbs’, i.e., vegetables, fruits, legumes, oatmeal
and other unprocessed whole grains. Moderate-carbohydrate diets are also better for those who wish to maximize gains in muscle mass. But when it comes to short-term fat loss, while maintaining and even gaining muscle, your best dietary approach is the proven and powerful
very low carbohydrate diet.

NOTE: The author of this article has no financial relationship with supplement companies mentioned in this article.


1. Nutr Metab (Lond). 2006 Jan 31;3:9
2. J Am Diet Assoc. 2001 Apr;101(4):411-20.
3. J Am Diet Assoc. 1980 Sep;77(3):264-70.
4. Am J Clin Nutr. 1971 Mar;24(3):290-6.
5. Metabolism. 2002 Jul;51(7):864-70.
6. Nutr Metab (Lond). 2004 Nov 8;1(1):13.
7. Am J Clin Nutr. 2006 Feb;83(2):260-74.