Research Supporting a Low-Carb Diet

Studies show that following a low-carbohydrate, high-fat diet results in weight loss, lower cholesterol, and stable blood glucose.

The table below compares two independent studies performed by Dr. Dean Ornish, who promotes a low-fat diet, and Dr. Robert Atkins, who supports weight loss through carbohydrate restriction.

Ornish and Atkins Diets Compared

INITIAL CONDITIONS	ORNISH (low fat)	ATKINS (low carbohydrate)
Age	56	55
Starting weight	201	195
Body Mass Index	28.4	28.1
DIET RESULTS	ORNISH (low fat)	ATKINS (low carbohydrate)
Cholesterol change	-24%	-13%
HDL (GOOD) Cholesterol	- 3%	+60%
Triglycerides (BAD)	+75%	-82%
Weight	-12%	-19%

Results of other studies...

• A number of short term studies, mostly in the 50's and 60's, showed a marked advantage in weight loss from high protein, low carbohydrate diets compared to diets higher in carbohydrate. (Chuck Forsberg, "Adiposity 101")
  
  
• Compared to high carbohydrate diets, a high protein low carbohydrate diet preserved lean body mass and improved glucose oxidation. (METABOLISM Dec 1994 43:12 1481-7)
  
  
• In the presence of carbohydrate, the preferred fuel is glucose and the capacity to mobilize fat is limited. Factors that increase blood glucose during dieting may stimulate insulin release and all the metabolic sequelae of circulating insulin. Fatty acid synthesis is activated and lipolysis is profoundly inhibited by insulin even at very low concentrations of the hormone. (Am J or Clin Nut 1992;56;217S-23S)
  
  
• In the obese NIDDM (Type II diabetes patients), ketones generated by low carbohydrate diets suppress hepatic glucose output and fasting blood sugar. (O619, IJO 1994 165)
  
  
• A Scottish study found lowering carbohydrate intake doubled weight loss, increased fat oxidation, and reduced metabolic slowdown compared to lowering fat intake.
  
  
• A study published in the June 6, 2007 issue of Science Daily concludes the followiong: "Although the purpose of both of these studies was to glean insights into metabolic physiology, our findings suggest that increased levels of FGF21 may be a potential mechanism behind low-carbohydrate diets' beneficial properties when it comes to lipid metabolism," says Maratos-Flier. "Diets that limit carbohydrates and eliminate transfats, and at the same time emphasize fiber and good fats, appear to be healthiest, especially among individuals who are predisposed to developing diabetes."

  This study was supported, in part, by grants from the National Institutes of Health and from Takeda Pharmaceuticals.
  
  

• "We treated obese subjects with high fat, low carbohydrate diets. If the carbohydrate content of the diet was not more than 50 to 60 g/day and the fat content approximately 150 g/day, an average daily weight reduction of 0.3 kg was achieved. The cholesterol and triglyceride concentrations in the serum, which had been raised at the beginning of the experiment, invariably showed a tendency towards normalization under this dietary program." (1973 American Journal of Clinical Nutrition, "Response of body weight to a low carbohydrate, high fat diet in normal and obese subjects")
  
  
• As reported in Newsday, (March, 2000), researchers at Schneider Children's Hospital in New Hyde Park, NY, found that overweight teens on a high-fat, high-protein diet lost more weight than adolescents on a traditional low-fat diet. The study, which included 22 people ages 12-18 who were 20-100 pounds overweight, found that those on the high-fat, high-protein diet lost an average of 19 pounds in 12 weeks, compared to those on a low-fat diet who lost an average of 8.5 pounds. The teens' cholesterol levels also improved, according Dr. Marc Jacobson, lead researcher and director of the Center for Atherosclerosis Prevention at the hospital. Overall cholesterol levels dropped in both groups, according to Nancy Copperman, the nutritionist who designed the diets. But triglycerides -- a kind of blood fat -- fell 33 percent in the high-fat, high-protein diet group, compared to 17 percent in the low- fat diet group, Copperman said. And levels of HDL, the so-called "good" cholesterol, also improved. Kidney and liver functions were not affected.
  
  
• Conference Report - North American Association for the Study of Obesity
  from Medscape Diabetes & Endocrinology

  Low-Carbohydrate, High-Protein Diets Physicians are often asked about the safety and efficacy of low-carbohydrate, high-protein diets. Unfortunately, very few controlled studies have evaluated these popular regimens. These diets, which are often high in fat, raise concerns about their effects on lipid levels. One such diet, the Atkins Diet, restricts carbohydrates and encourages unlimited consumption of protein and fat. Preliminary results were presented from a 3-center (University of Pennsylvania, University of Colorado, Washington University) randomized controlled trial comparing the Atkins Diet with a conventional low-fat, high-carbohydrate plan that restricted daily caloric intake to 1200-1500 kcal for women and 1500-1800 kcal for men.[10] The study included 63 obese (BMI 33.8 ± 3.4 kg/m2) males and females who were randomized to 1 of the 2 diets. Subjects received an initial session with a dietitian to explain the assigned diet program. At 12 weeks, the researchers found that the Atkins group had a lower rate of attrition (12%) compared with that of the conventional program (30%). In addition, subjects in the Atkins group lost significantly more weight (8.5 ± 3.7%) compared with the conventional group (3.7 ± 4.0%). In terms of serum lipids, the Atkins group demonstrated slight increases in total cholesterol (TC; 2.2 ± 16.6%) and low-density lipoprotein (LDL) cholesterol (6.6 ± 20.7%), whereas the conventional group showed significant decreases in these measures (TC -8.2 ± 11.5%; LDL -11.1 ± 19.4%). High-density lipoprotein (HDL) cholesterol significantly increased in the Atkins group (11.5 ± 20.6%) but did not change in the conventional group, whereas triglycerides showed a significant decrease for the Atkins group (-21.7 ± 27.9%) and no change in the conventional group. At 26 weeks, these changes persisted in both groups even though the sample size was smaller. The researchers concluded that the Atkins Diet produced favorable effects on weight, HDL, triglycerides, and retention compared with a conventional low-fat, low-calorie program, whereas the conventional plan was associated with more favorable effects on TC and LDL cholesterol.

  A similar randomized-controlled trial from Duke University was also presented at the conference. The researchers in this study also compared the effects of a low-carbohydrate (LC) diet with a low-fat, low-calorie (LF) program. This study included 120 obese (mean BMI 34 kg/m2) males and females, who all received group treatment for their respective diet programs. At 6 months, both groups had similar rates of attrition, but the LC group lost considerably more weight (13.3 ± 4.6%) compared with the LF group (8.6 ± 5.9%). In addition, the LC group lost significantly more fat mass than the LF group (-9.7 kg for the LC group and -6.4 kg for the LF group). Both groups showed decreases in triglycerides, with the LF group also showing a significant decrease in total cholesterol (-13.5 mg/dL). The LC group showed significant increases in HDL and a significant decrease in Chol/HDL ratio. This pattern of results was similar to those of the 3-center study described above.
  
  

• Heart Disease Related to Glycemic Load

  Simin Liu, Walter C Willett, Meir J Stampfer, Frank B Hu, Mary Franz, Laura Sampson, Charles H Hennekens and JoAnn E Manson

  From the Departments of Epidemiology and Nutrition, the Harvard School of Public Health; the Channing Laboratory; and the Division of Preventive Medicine, the Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston.

  Background: Little is known about the effects of the amount and type of carbohydrates on risk of coronary heart disease (CHD).

  Objective: The objective of this study was to prospectively evaluate the relations of the amount and type of carbohydrates with risk of CHD.

  Design: A cohort of 75521 women aged 38–63 y with no previous diagnosis of diabetes mellitus, myocardial infarction, angina, stroke, or other cardiovascular diseases in 1984 was followed for 10 y. Each participant's dietary glycemic load was calculated as a function of glycemic index, carbohydrate content, and frequency of intake of individual foods reported on a validated food-frequency questionnaire at baseline. All dietary variables were updated in 1986 and 1990.

  Results: During 10 y of follow-up (729472 person-years), 761 cases of CHD (208 fatal and 553 nonfatal) were documented. Dietary glycemic load was directly associated with risk of CHD after adjustment for age, smoking status, total energy intake, and other coronary disease risk factors. The relative risks from the lowest to highest quintiles of glycemic load were 1.00, 1.01, 1.25, 1.51, and 1.98 (95% CI: 1.41, 2.77 for the highest quintile; P for trend < 0.0001). Carbohydrate classified by glycemic index, as opposed to its traditional classification as either simple or complex, was a better predictor of CHD risk. The association between dietary glycemic load and CHD risk was most evident among women with body weights above average [ie, body mass index (in kg/m²)

  Conclusion: These epidemiologic data suggest that a high dietary glycemic load from refined carbohydrates increases the risk of CHD, independent of known coronary disease risk factors.

Some excerpts from "Adiposity 101," by Chuck Forsberg

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