Low-carbohydrate diets have become one of, if not the most, popular method of losing weight in recent years. But what exactly is a “low carbohydrate” diet? There are so many varying definitions of what a low carbohydrate diet is, that it has become difficult to pinpoint exactly what a person means when they say that they are on one. Most of the studies on low carbohydrate diets have them as low as eight percent of total energy intake, but some have them as high as 30 percent. In terms of grams, a low carbohydrate diet is usually defined as less than approximately 60 grams of carbohydrates per day (1).
It is a common concern of the general public and health professionals to question the safety of low carbohydrate diets. Some think that a high intake of dietary fat will wreak havoc on a persons triglyceride and cholesterol levels. Another concern is due to increase consumption of animal products, there will be a higher intake of dietary saturated fat and total dietary fat.
The following will specifically focus on the safety of low-carbohydrate diets in terms of blood lipid markers, and their effect on cardiovascular disease risk:
Safety of Low-Carbohydrate diets - Part 1:
When discussing low carbohydrate diets, a common concern is the effect of this diet regimen on cardiovascular disease risk. One consistent finding in the research is that low carbohydrate diets can significantly lower triglyceride levels. This is the opposite of what a layperson would think, because it would seem that a higher intake of fat (when one is on a diet low in carbohydrates) would cause a higher blood lipid (fat) level. However, the physiology involved is much more complex than a mere assumption of a linear relationship between dietary fat and blood lipid levels. In terms of cholesterol, there is a trend in the research that shows increases in HDL-cholesterol while LDL-cholesterol changes are variable with no consistent trends or findings (1-4).
What does the research have to say?
A six month study by Samaha et al (2003), examining low-carbohydrate diets versus low-fat diets in severely obese subjects, showed greater weight loss and improvements in triglycerides and insulin sensitivity in the low-carbohydrate group with no adverse effects on serum lipids. Yet, it should be noted that the low fat group also had no adverse effects on serum lipids (2). In a one-year follow-up of the aforementioned study, the decreases in triglycerides were maintained in the low-carbohydrate group. The study does note that future studies are needed to evaluate long-term cardiovascular outcomes (3). However, this one year study does show promise that low-carbohydrate diets are safe to use.
A rare, two year study by Yancy et al (2004), examining low-carbohydrate diets versus low-fat diets in relatively healthy, obese, hyperlipidemic subjects, showed improved outcomes in triglyceride and HDL-cholesterol levels while LDL-cholesterol remained stable. There were also no significant differences observed in blood pressure. One limitation of this study was that the low-carbohydrate group was given nutritional supplements, one containing fish oil, which may have had some effect on the final outcome of this study, especially because the study was two years long. The dropout rates of this study are of particular interest. Dropout rates were 24 percent for the low-carbohydrate group and 43 percent for the low-fat group. This is because there were meetings twice a month and many participants had to drop out because they could not make the meetings. In terms of side effects and safety of a low-carbohydrate diet, it should be noted that three participants of the low-carbohydrate group dropped out because of adverse events related to either elevated LDL-cholesterol levels or feelings of shakiness and uneasiness. Also, in terms of reported side effects, symptomatic side effects occurred more frequently in the low-carbohydrate group than the low-fat group and included constipation, headache, bad breath, muscle cramps, diarrhea, general weakness, and rash (4). The reporting of side effects was a strong aspect of this study and shows some of the side effects that can occur when on a low-carbohydrate diet. Some studies, which seem to have a bias in favor of low-carbohydrate diets, neglect to report the symptomatic side effects.
1. Crowe TC. Safety of low-carbohydrate diets. Obesity reviews. 2005;6:235-245
2. Samaha FF, Iqbal N, Seshadri P, Chicano KL, Daily DA, McGrory J, Williams T, Williams M, Gracely EJ, Stern L. A low-carbohydrate as compared with a low-fat diet in severe obesity. N Engl J Med. 2003;348:2074-2081.
3. Stern L, Iqbal N, Seshadri P, Chicano KL, Daily DA, McGrory J, Williams M, Gracely EJ, Samaha FF. The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial. Ann Int Med. 2004;140:778-785.
4. Yancy WS, Olsen MK, Guyton JR, Bakst RP, Westman EC. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia. Ann Int Med. 2004;140:769-777.