Low Carbohydrate Diets for Weight Loss: Myth or Reality?
By Theresa Glanvitte Ph.D, PDt, Mount St. Vincent University, NS

Low carbohydrate (CHO), high protein diets, promising quick weight loss without hunger or self-deprivation, are the rage. This approach to weight loss is not new and regularly resurfaces in the popular press, each time with a new twist, supported by testimonials and anecdotal reports rather than scientific evidence. The underlying premise of the diets is that consumption of CHO-rich foods stimulates over-production of insulin, the hormone responsible for the transport and storage of glucose and, under certain conditions, fat. Since protein-rich foods are reported to have less impact on insulin secretion, by substituting protein-rich foods for CHO-rich foods in these diets, it is proposed that stored fat is used for energy.

Popular Low-CHO Diets
Atkins Diet Revolution • Limits CHO to less than 20g/day (=1 slice of bread) to promote ketosis	Sugar Busters • Focus on low-glycemic index CHO • Fruit consumed before a meal only
Carbohydrate Addicts Diet • Limits CHO to 1 or 2 servings/day	Schwartzbein • Combining protein and non-starchy CHO proposed to prevent storage as fat
Montignac Diet • Focus on low-glycemic index foods; avoid fat and CHO together in a meal	Suzanne Somers • Don't eat fat and CHO together • Wait 20 min between eating fruit and other CHO
Protein Power • Limits CHO to 40 g/day; protein from 240 to 480 g/day	The Zone • CHO 40% of total energy, balanced with protein and fat within each meal

Body fatness reflects the balance between energy intake and expenditure. Proponents of CHO-restricted diets claim that weight loss can occur without a reduction in total energy intake. However, analysis of several CHO-restricted diets reveals that they are energy-reduced, often containing 800 -1200 kcal per day, similar to conventional reducing diets. This is because the types of food and combinations allowed are very prescriptive. For example, one diet claims you can eat all the steak, bacon and eggs you want, but severely restricts consumption of grains, dairy, fruits and vegetables, thereby limiting total food consumption.

Research comparing an energy-reduced (1200 kcal/day) CHO-restricted diet (75g/ day) with a conventional carbohydrate-rich diet (225 g/day) that similarly restricts energy intake, showed that both approaches produce weight loss, but that overall decrease in the early phase of dieting was greater with CHO restriction (1). This was largely due to sodium excretion and water loss associated with utilization of stored glycogen. Both of these components of weight loss will be rapidly regained when normal food intake is resumed, and glycogen stores are replenished. Regardless of whether the energy restricted diet is CHO-restricted or CHO-rich, the loss of body fat, as a component of the loss of body weight, is the same (2,3).

Significant and sustained weight loss is a difficult goal. The reward of rapid weight loss during early CHO-restriction may increase compliance. Likewise, extreme CHO restriction can produce ketosis marked by loss of appetite - which can be an additional compliance factor. Over the long term, this type of diet is monotonous and difficult to maintain. Health concerns include possible deficiencies in calcium, potassium, and the B vitamins. The impact of excess nitrogen intake may also worsen pre-existing conditions such as gout, liver and kidney disease.

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REFERENCES

1. Shah, M. Garg, A. Diabetes Care 1996;10:1142-1152

2. BaBa NH et al. Int J Obes Relat Metab Disord 1999;23:1202-1206

3. Golay A et al. Am J Clin Nutr 1996;63:174-178