23 studies on low-carb and low-fat diets part 1

There are few things that have been debated as much as which is better: a low-carb diet or a low-fat diet. Some believe that increasing the amount of fat in the diet can lead to all kinds of health problems and especially heart disease.

This is the position taken by mainstream health organizations. These organizations generally recommend limiting the amount of dietary fat to less than 30% of total calories (which is equivalent to a low-fat diet).

Over the past 11 years, however, an increasing number of studies have challenged this low-fat diet approach. Many health experts now believe that a low-carbohydrate diet (which is richer in fat and protein ) is a much better option for treating obesity and other chronic Western diseases.

This article analyzes data from 23 studies comparing low-carb and low-fat diets. All of these studies are randomized trials - the scientific gold standard. All of these studies were published in reputable peer-reviewed journals.

The studies

Most of the studies were conducted with people who suffered from health problems including overweight/obesity, type 2 diabetes and metabolic syndrome. It is important to remember that these are the biggest health problems in the world.

The primary outcomes usually include weight loss, as well as a reduction in common risk factors such as total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides and blood sugar levels.

Readers who are less interested in the details of the studies and more interested in the evaluation of the results of these studies can also skip the first part of this article and go straight to the second part of this article.

1 Foster GD, et al. A randomized trial of a low-carbohydrate diet for obesity.New England Journal of Medicine, 2003.

Details: 63 subjects were randomly assigned to a low-fat diet or low-carbohydrate diet group. The amount of calories in the low-fat group was limited. The study ran for 12 months.

Weight loss: The group on the low-carbohydrate diet lost 7.3% of body weight, more than the low-fat group, which lost 4.5% of body weight. The difference was statistically significant after 3 and 6 months, but not after 12 months.

Conclusion: Weight loss was higher in the low-carbohydrate group - significant at the 3 and 6 month mark, but not at the 12 month mark. The low-carbohydrate group had greater improvements in blood triglyceride levels and HDL levels, but other biomarkers were similar in both groups.

2 Samaha FF, et al. A low-carbohydrate as compared with a low-fat diet in severe obesity. New England Journal of Medicine, 2003.

Details: 132 subjects with severe obesity (BMI > 43) were randomly assigned to either a low-fat or low-carbohydrate diet group. Many of the subjects suffered from metabolic syndrome or type 2 diabetes. The calorie intake of the low-fat group was restricted. The duration of the study was 6 months.

Weight loss: The low-carbohydrate group lost an average of 5.8 kilos, while the low-fat group lost only 1.9 kilos. The difference was statistically significant.

Conclusion: The low-carbohydrate group lost significantly more weight (about three times as much). There were also statistically significant differences in various biomarkers:

• Triglyceride levels decreased by 38 mg/dL in the low-carbohydrate group and by 7 mg/dL in the low-fat group.
• Insulin sensitivity improved in the low-carbohydrate group and worsened slightly in the low-fat group.
• Fasting blood glucose levels decreased by 26 mg/dL in the low-carbohydrate group and only 5 mg/dL in the low-fat group.
• Insulin levels decreased by 27% in the low-carb group and increased slightly in the low-fat group.

Overall, the low-carbohydrate diet had significantly more positive effects on weight and key biomarkers in this group of severely overweight individuals.

3 Sondike SB, et al. Effects of a low-carbohydrate diet on weight loss and cardiovascular risk factor in overweight adolescents. The Journal of Pediatrics, 2003.

Details: 30 overweight adolescents were randomly divided into two groups: a low-carbohydrate group and a low-fat group. This study lasted for 12 weeks. Neither group was instructed to restrict their calorie intake.

Weight loss: the low-carbohydrate group lost 9.9 kilos, while the low-fat group lost 4.1 kilos. The difference was statistically significant.

Conclusion: The low-carbohydrate group lost significantly more weight (2.3 times as much) and had significantly reduced triglyceride and non-HDL cholesterol levels. LDL and total cholesterol levels decreased only in the low-fat group.

4 Brehm BJ, et al. A randomized trial comparing a very low carbohydrate diet and a calorie-restricted low fat diet on body weight and cardiovascular risk factors in healthy women. The Journal of Clinical Endocrinology & Metabolism, 2003.

Details: 53 healthy but overweight women were divided into a low-fat diet group and a low-carbohydrate diet group. The calorie intake of the low-fat group was restricted. The study ran for 6 months.

Weight loss: The women in the low-carbohydrate group lost an average of 8.5 kilos, while the women in the low-fat group lost an average of 3.9 kilos. The difference was statistically significant after 6 months.

Conclusion: The low-carbohydrate group lost more weight (2.2 times as much) and showed significant reductions in blood triglyceride levels. HDL cholesterol levels improved slightly in both groups.

5 Aude YW, et al. The national cholesterol education program diet vs a diet lower in carbohydrates and higher in protein and monounsaturated fat.Archives of Internal Medicine, 2004.

Details: 60 overweight subjects were randomly assigned to a low-carbohydrate group with a high monounsaturated fat intake or a low-fat diet group based on the National Cholesterol Education Program (NCEP). The calorie intake of both groups was restricted and the study lasted for 12 weeks.

Weight loss: The low-carbohydrate group lost an average of 6.2 kg, while the low-fat group lost only 3.4 kilos. The difference was statistically significant.

Conclusion: The low-carbohydrate group lost 1.8 times as much weight. There were also several notable changes in biomarkers:

• Waist-to-hip ratio is a marker of the amount of abdominal fat. This marker improved slightly in the low-carbohydrate group - but not in the low-fat group.
• Total cholesterol levels improved in both groups.
• Triglyceride levels decreased by 42 mg/dL in the low-carbohydrate group and by 15.3 mg/dL in the low-fat group.
• LDL particle size increased by 4.8 nm in the low-carbohydrate group and the percentage of small, dense LDL particles decreased by 6.1%, while no changes were observed in the low-fat group.

Overall, the low-carbohydrate group lost more weight and showed greater improvements in several important risk factors for cardiovascular disease.

6 Yancy WS Jr, et al. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia. Annals of Internal Medicine, 2004.

Details: 120 overweight subjects with elevated blood lipid levels were randomly assigned to a low-carbohydrate or low-fat diet group. The calorie intake of the low-fat group was restricted. The study lasted for 24 weeks.

Weight loss: The low-carbohydrate group lost 9.4 kg of body weight, compared to 4.8 kg in the low-fat group.

Conclusion: The low-carbohydrate group lost significantly more weight and showed greater improvements in triglyceride levels and HDL cholesterol levels.

7 JS Volek, et al. Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women. Nutrition & Metabolism (London), 2004.

Details: this was a randomized cross-over design study of 28 overweight/obese subjects over a period of 30 days (for women) and 50 days (for men) for each diet. The subjects followed a very low-carbohydrate diet and a low-fat diet in succession.

Weight loss: The low-carbohydrate group lost significantly more weight, which was especially true for men. This was despite the fact that the subjects in the low-carbohydrate group consumed more calories than the subjects in the low-fat group.

Conclusion: The low-carbohydrate group lost more weight. The men who followed a low-carbohydrate diet lost three times as much abdominal fat as the men who followed a low-fat diet.

8. Meckling KA, et al. Comparison of a low-fat diet to a low-carbohydrate diet on weight loss, body composition, and risk factors for diabetes and cardiovascular disease in free-living, overweight men and women. The Journal of Clinical Endocrinology & Metabolism, 2004.

Details: 40 overweight subjects were randomly assigned to a low-carbohydrate diet group or a low-fat diet group. The calorie intake was the same in both groups. #

Weight loss: The low-carbohydrate group lost 7.0 kg and the low-fat group lost 6.8 kg. The difference was statistically significant.

Conclusion: Both groups lost a similar amount of weight. However, there were some notable differences in biomarkers:

• Blood pressure decreased in both groups - both systolic and diastolic blood pressure.
• Total and LDL cholesterol levels decreased only in the low-fat group.
• Triglyceride levels fell in both groups.
• HDL cholesterol levels increased in the low-carbohydrate group and decreased in the low-fat group.
• Blood glucose levels decreased in both groups, but the low-carbohydrate group showed a greater reduction in insulin levels, indicating increased insulin sensitivity.

9 Nickols-Richardson SM, et al. Perceived hunger is lower and weight loss is greater in overweight premenopausal women consuming a low-carbohydrate/high-protein vs high-carbohydrate/low-fat diet. Journal of the American Dietetic Association, 2005.

Details: 28 overweight premenopausal women consumed either a low-carbohydrate or a low-fat diet for a period of 6 weeks. The calorie intake of the low-fat group was restricted.

Weight loss: The women in the low-carbohydrate group lost 6.4 kg while the women in the low-fat group lost only 4.2 kg. The results were statistically significant.

Conclusion: The low-carbohydrate diet resulted in significantly greater weight loss and also reduced hunger better compared to the low-fat diet.

10. Daly ME, et al. Short-term effects of severe dietary carbohydrate-restriction advice in type 2 diabetes. Diabetic Medicine, 2006.

Details: 102 patients with type 2 diabetes were randomly assigned to a group following either a low-fat diet or a low-carbohydrate diet over a 3-month period. The low-fat group was instructed to reduce portion size.

Weight loss: The low-carbohydrate group lost 3.55 kg, while the low-fat group lost only 0.92 kg. The difference was statistically significant.

Conclusion: The low-carbohydrate group lost more weight and showed greater improvements in the ratio of total cholesterol to HDL cholesterol. No differences in triglyceride levels, blood pressure or HbA1c (a marker of blood glucose levels) were observed between the groups.

11 McClernon FJ, et al. The effects of a low-carbohydrate ketogenic diet and a low-fat diet on mood, hunger, and other self-reported symptoms.Obesity (Silver Spring), 2007.

Details: 119 overweight subjects were randomly assigned to a low-carbohydrate, ketogenic diet or a low-fat, calorie-restricted diet. The study ran for a period of 6 months.

Weight loss: The low-carbohydrate group lost 12.9 kg, while the low-fat group lost only 6.7 kg.

Conclusion: The low-carbohydrate group lost almost twice as much weight and experienced less hunger.

12 Gardner CD, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study. The Journal of The American Medical Association, 2007.

Details: 311 overweight/obese premenopausal women were randomly assigned to one of 4 groups that followed the following diets:

• A low-carbohydrate Atkins diet
• A low-fat vegetarian Ornish diet
• The Zone diet
• The LEARN diet

Calorie intake was restricted in the groups following the Zone and LEARN diets.

Weight loss: The Atkins had lost the most weight after 12 months (4.7 kg), while subjects on the Ornish diet lost 2.2 kg, subjects on the Zone diet lost 1.6 kg and subjects on the LEARN diet lost 2.6 kg. However, the difference was not statistically significant after 12 months.

Conclusion: The Atkins group lost the most weight, even though the difference was not statistically significant. The Atkins group also showed the greatest improvements in blood pressure, triglyceride levels and HDL cholesterol levels. In the LEARN and Ornish groups, reductions in LDL cholesterol levels were observed after 2 months, but this effect diminished thereafter.

13 Halyburton AK, et al. Low- and high-carbohydrate weight-loss diets have similar effects on mood but not cognitive performance. American Journal of Clinical Nutrition, 2007.

Details: 93 overweight/obese subjects were randomly assigned to either a low-carbohydrate, high-fat diet group or a low-fat, low-carbohydrate diet group. The calorie intake of both groups was restricted.

Weight loss: The low-carbohydrate group lost 7.8 kg while the low-fat group lost 6.4 kg. The difference was statistically significant.

Conclusion: The low-carbohydrate group lost more weight. Similar improvements in mood were observed in both groups, but cognitive performance improved more in the low-fat diet.

14 Dyson PA, et al. A low-carbohydrate diet is more effective in reducing body weight than healthy eating in both diabetic and non-diabetic subjects.Diabetic Medicine, 2007.

Details: 13 diabetic and 13 non-diabetic subjects were randomized into a group following a low-carbohydrate diet and a group following a classic healthy diet as defined by the Diabetes UK Recommendations (a low-calorie, low-fat diet). The study lasted 3 months.

Weight loss: The low-carbohydrate group lost 6.9 kg, while the low-fat group lost only 2.1 kg.

Conclusion: The low-carbohydrate group lost more weight (about 3 times as much). No differences in other markers were observed between the two groups.

15 Westman EC, et al. The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus. Nutrion & Metabolism (London), 2008.

Details: 84 obese subjects suffering from type 2 diabetes were randomly divided into a group following a low-carbohydrate, ketogenic diet and a group following a low-glycemic index diet. The duration of the study was 24 weeks.

Weight loss: The low-carbohydrate group lost more weight (11.1 kg) than the low-glycemic group (6.9 kg).

Conclusion: The low-carbohydrate group lost significantly more weight than the low-glycemic group. There were also several other important differences:

• Hemoglobin A1c levels decreased by 1.5% in the low-carbohydrate group and 0.5% in the low-glycemic group.
• HDL cholesterol levels increased only in the low-carbohydrate group - by 5.6 mg/dL.
• Diabetes medication could be either reduced or completely discontinued in 95.2% of the members of the low-carbohydrate group, while this was only possible in 62% of the members of the low-glycemic group.
• Many other health markers such as blood pressure and triglyceride levels improved in both groups, although the differences between the groups were not statistically significant.

The second part will look at the remaining 8 studies on the topic, which will be followed by a summary and analysis of the study results.

Source: https://www.healthline.com/nutrition/23-studies-on-low-carb-and-low-fat-diets#section9