many people traditionally choose a low-fat diet and count calories to lose weight.
low-carb and low-fat diets have comparable weight loss effects? low-fat or low-carb diet, which is healthier? studies show that low-carb and low-fat diets have comparable weight loss effects? the health benefits of a low carb and ketogenic diet? low-carb diets and obesity?
when it comes to weight loss, nutritionists often argue about "carbohydrates vs. fats."
most mainstream health organizations believe that a fat-rich diet can lead to health problems, especially heart disease.
they tend to recommend a low-fat diet that limits dietary fat to less than 30% of total calories.
however, a growing body of research has been challenging low-fat methods.
many people now believe that a low-carb diet higher in fat and protein may be more effective in treating and preventing obesity and other diseases.
this paper analyzed data from 23 studies comparing low-carb and low-fat diets.
all studies were randomized controlled trials and appeared in respected peer-reviewed journals.
study
many studies comparing low-carb and low-fat diets have targeted the following populations:
- corpulent
- type 2 diabetes
- metabolic syndrome
researchers typically measure the following factors:
- weight loss
- cholesterol levels
- triglycerides
- blood sugar levels
1. Foster, GD, etc. A randomized trial of a low-carb diet for obesity. New England Journal of Medicine, 2003.
details: 63 obese adults followed a low-fat or low-carbohydrate diet for 12 months. the low-fat group restricts calories.
weight loss: after 6 months, the low-carb group lost 7% of its body weight, while the low-fat group lost 3%. the difference was statistically significant at 3 and 6 months, but not at 12 months.
Conclusion: The low-carb group lost more weight, with significant differences between 3 and 6 months and not significant at 12 months. The low-carbohydrate group had greater improvements in blood triglycerides and HDL (good cholesterol), but other biomarkers were similar between the group.
2. Samaha, FF, etc. Low carbohydrate compared to a low-fat diet for severe obesity. New England Journal of Medicine, 2003.
Details: In this study, 132 people who were severely obese (with an average BMI of 43) followed a low-fat or low-carb diet for 6 months. Many people have metabolic syndrome or type 2 diabetes. Calorie intake is limited for low-fat dieters.
weight loss: the low-carb group lost an average of 12.8 pounds (5.8 kilograms), while the low-fat group lost only 4.2 pounds (1.9 kilograms). the difference is statistically significant.
Conclusion: those who followed a low-carb diet lost about three times as much weight than those on a low-fat diet.
there are also statistically significant differences in several biomarkers:
- Triglycerides decreased by 38 mg/dL in the low-carbohydrate group and 7 mg/dL in the low-fat group.
- insulin sensitivity improved in low-carbohydrate diets, but insulin sensitivity in low-fat diets deteriorated slightly.
- Fasting blood glucose levels decreased by 26 mg/dL in the low-carb group, but only 5 mg/dL decreased in the low-fat group.
- insulin levels decreased by 27% in the low-carb group, but there was a slight increase in insulin levels in the low-fat group.
overall, in this study, a low-carb diet produced more benefits for body weight and key biomarkers.
3. Sondike, SB, etc. Effects of low-carbohydrate diets on weight loss and cardiovascular risk factors in overweight adolescents. Journal of Trusted Source Pediatrics, 2003.
details: 30 overweight adolescents followed a low-carb diet or a low-fat diet for 12 weeks. neither group restricted their calorie intake.
weight loss: people on a low-carb diet lost 21.8 pounds (9.9 kilograms), while people on a low-fat diet lost only 9 pounds (4.1 kilograms). the difference is statistically significant.
Conclusion: The low-carb group lost 2.3-fold weight and significantly reduced triglyceride and non-high-density lipoprotein (non-HDL) cholesterol levels. Total cholesterol and low-density lipoprotein (LDL)—or "bad" cholesterol—declined only in the low-fat group.
4. Brehm, BJ, et al. One randomized trial compared the effects of very low-carbohydrate diets and calorie-restricted low-fat diets on weight and cardiovascular risk factors in healthy women. Journal of Clinical Endocrinology and Metabolism, 2003.
Details: 53 obese but in good health followed a low-fat or low-carb diet for 6 months. the low-fat group limited their calorie intake.
Weight loss: People in the low-carb group lost an average of 18.7 pounds (8.5 kilograms), while those in the low-fat diet group lost an average of 8.6 pounds (3.9 kilograms). the difference was statistically significant at 6 months.
Conclusion: the low-carb group lost 2.2 times more weight than the low-fat group. blood lipids improved significantly in each group, but there were no significant differences between the groups.
5. Odd, YW, et al. National Cholesterol Education Program diet versus diets low in carbohydrates and high in protein and monounsaturated fats: a randomized trial of trusted sources. Archives of Internal Medicine, 2004.
Details: 60 overweight people either followed a low-carb diet high in monounsaturated fats or a low-fat diet under the National Cholesterol Education Program (NCEP). They followed a diet for 12 weeks
both groups limited their calorie intake.
weight loss: the low-carb group lost an average of 13.6 pounds (6.2 kilograms), while the low-fat group lost 7.5 pounds (3.4 kilograms). the difference is statistically significant.
Conclusion: the low-carb group lost 1.8-fold weight and underwent some biomarker changes:
- the waist-to-hip ratio is a sign of abdominal fat. this marker improved slightly in the low-carb group, but not in the low-fat group.
- total cholesterol improved in both groups.
- Triglycerides decreased by 42 mg/dL in the low-carbohydrate group and 15.3 mg/dL in the low-fat group. However, the differences between groups were not statistically significant.
- The LDL particle size of the low-carb group increased by 4.8 nm, while the percentage of small, dense LDL particles decreased by 6.1%. There were no significant differences in the low-fat group and no statistically significant changes between groups
overall, the low-carb group lost more weight and improved in several important risk factors for cardiovascular disease.
6. Yancy, WS Jr., et al. Low-carbohydrate, ketogenic diets and low-fat diets treat obesity and hyperlipidemia. Trusted Source Internal Medicine Yearbook, 2004.
Details: in this study, 120 people who were overweight and high in blood lipids followed a low-carbohydrate or low-fat diet for 24 weeks. the low-fat group limited their calorie intake.
Weight loss: people in the low-carb group lost 20.7 pounds (9.4 kilograms) and those in the low-fat group lost 10.6 pounds (4.8 kilograms).
Conclusion: people in the low-carbohydrate group lost significant weight, and the improvement of blood triglycerides and hdl (good) cholesterol was greater.
7. Volek, JS, etc. Energy-restricted extremely low-carb and low-fat diets compared to overweight men and women with weight loss and body composition. Trusted Source Nutrition and Metabolism (London), 2004.
Details: in a study involving 28 obese or overweight individuals, women followed a very low-carb or low-fat diet for 30 days, and men followed one of these diets for 50 days. both diets limit calories.
Weight loss: people in the low-carb group lost significantly more weight. this is especially true for men, even if they consume more calories than the low-fat group.
Conclusion: people in the low-carb group lost more weight than those in the low-fat group. men on low-carb diets lost three times as much belly fat as men on low-fat diets.
8. Meckling, KA, etc. Low-fat versus low-carb diets compared to free living, weight loss in overweight men and women, body composition, and risk factors for diabetes and cardiovascular disease. Journal of Clinical Endocrinology and Metabolism, 2004.
details: 40 overweight people followed a low-carb or low-fat diet for 10 weeks. the calorie intake was the same for each group.
Weight loss: The low-carb group lost 15.4 pounds (7.0 kilograms) and the low-fat group lost 14.9 pounds (6.8 kilograms). the difference was not statistically significant.
conclusion: similar amounts of weight loss were lost in both groups, and the following also occurred:
- blood pressure was reduced in both groups, systolic and diastolic.
- total cholesterol and ldl (bad) cholesterol declined only in the low-fat group.
- triglycerides decreased in both groups.
- hdl (good) cholesterol rose in the low-carb group but decreased in the low-fat group.
- blood sugar dropped in both groups, but insulin levels decreased in only the low-carbohydrate group. this indicates that insulin sensitivity is improved.
9. Nickols-Richardson, SM, etc. Overweight premenopausal women who consume low-carb/high-protein diets have lower hunger and more weight loss compared to high-carb/low-fat diets. Journal of the American Dietetic Association, 2005.
details: 28 overweight women who have not yet entered menopause have consumed a low-carb or low-fat diet for 6 weeks. low-fat diets limit calories.
Weight loss: the low-carb group lost 14.1 pounds (6.4 kilograms), while the low-fat group lost 9.3 pounds (4.2 kilograms). the results are statistically significant.
Conclusion: low-carb diets have significantly more weight loss and less hunger than low-fat diets.
10. Daly, ME, etc. Severe dietary carbohydrate restrictions are recommended for short-term effects on type 2 diabetes. Trusted Source Diabetes Medicine, 2006.
Details: in this study, 102 people with type 2 diabetes received a 3-month low-carb or low-fat diet recommendation. people in the low-fat group are advised to reduce portion size.
weight loss: the low-carb group lost 7.8 pounds (3.55 kilograms), while the low-fat group lost only 2 pounds (0.92 kilograms). the difference is statistically significant.
Conclusion: The low-carb group lost more weight and improved the total cholesterol/HDL ratio. There were no differences in triglycerides, blood pressure, or HbA1c (markers of blood glucose levels) between the two groups.
11. McLeanon, FJ, etc. Effects of low-carb ketogenic and low-fat diets on mood, hunger, and other self-reported symptoms. Trusted Source Obesity (Silver Springs), 2007.
Details: in the study, 119 overweight people followed a low-carb, ketogenic diet, or a calorie-restricted, low-fat diet for 6 months.
Weight loss: people in the low-carb group lost 28.4 pounds (12.9 kilograms), while those in the low-fat group lost 14.7 pounds (6.7 kilograms).
Conclusion: the low-carb group had almost tripled its weight and felt less hungry.
12. Gardner, CD, etc. Comparison of weight changes and associated risk factors in premenopausal overweight women on the Atkins, Zone, Ornish, and LEARN diets: A TO Z Weight Loss Study. Journal of the American Medical Association, 2007.
Details: in the study, 311 women who did not experience menopause and were overweight or obese followed one of the following four diets:
- low-carb atkins diet
- Low-fat vegetarian Ornish diet
- regional diets
- learn to eat
Zone and LEARN are calorie restricted.
Weight loss: The Atkins group lost the most weight at 12 months —10.3 pounds (4.7 kg), compared to 4.9 pounds (2.2 kg) in the Ornish group, 3.5 pounds (1.6 kg) in the Zone group, and 5.7 pounds (2.6 kg) in the LEARN group.
however, the difference was not statistically significant at 12 months.
Conclusion: The Atkins group lost the most weight, but the difference was not statistically significant. The Atkins group had the greatest improvements in blood pressure, triglycerides, and HDL (good) cholesterol levels. Those who followed a low-fat diet, LEARN or Ornish, lowered their LDL (bad) cholesterol at 2 months, but then the effects diminished.
13. Halliburton, AK, etc. Low-carb and high-carb weight loss diets have a similar effect on mood, but no effect on cognitive performance. Trusted Source American Journal of Clinical Nutrition, 2007.
Details: 93 people who were overweight or obese followed a low-carb, high-fat diet or a low-fat, high-carb diet for 8 weeks. both groups restrict calories.
Weight loss: the low-carb group lost 17.2 pounds (7.8 kilograms) and the low-fat group lost 14.1 pounds (6.4 kilograms). the difference is statistically significant.
Conclusion: the low-carb group lost more weight. mood improved similarly in both groups, but processing speed (a measure of cognitive ability) was further improved in a low-fat diet.
14. dyson, pennsylvania, etc. in both diabetic and non-diabetic subjects, a low-carb diet was more effective at weight loss than a healthy diet. trusted source diabetes medicine, 2007.
details: 13 diabetics and 13 non-diabetics followed a low-carb diet or a "healthy diet" diet. this is a low-fat diet recommended by the british diabetes association to restrict calories. the study lasted 3 months.
Weight loss: people in the low-carb group lost an average of 15.2 pounds (6.9 kilograms), while those in the low-fat group lost an average of 4.6 pounds (2.1 kilograms).
Conclusion: the low-carb group lost three times as much body weight as the low-fat group. there are no differences in any other markers between groups.
15. Westman, EC, etc. Effects of low-carbohydrate, ketogenic, and low glycemic index diets on glycemic control in type 2 diabetes. Trusted Source Nutrition and Metabolism (London), 2008.
Details: 84 obese and type 2 diabetics followed a low-carb, ketogenic, or calorie-restricted, low-glycemic diet for 24 weeks.
Weight loss: the low-carb group lost more weight — 24.4 pounds (11.1 kilograms) — than the low-glycemic group — 15.2 pounds (6.9 kilograms).
Conclusion: people in the low-carb group lost more weight than those in the low-glycemic group. furthermore:
- Hemoglobin A1c decreased by 1.5% in the low-carbohydrate group and 0.5% in the hypoglycemic group.
- hdl (good) cholesterol increased by only 5.6 mg/dl in the low-carb group.
- diabetes medications were reduced or eliminated in 95.2% of the low-carb group, compared to 62% in the hypoglycemic group.
- blood pressure, triglycerides, and other indicators improved in both groups, but there were no statistically significant differences between the groups.
16. Shai, I. et al. Lose weight with a low-carb, Mediterranean, or low-fat diet. New England Journal of Medicine, 2008.
details: in this study, 322 obese people followed one of three diets:
- low-carb diet
- calorie-restricting, low-fat diets
- a mediterranean diet that restricts calories
they followed a dietary habit for 2 years.
Weight loss: 10.4 pounds (4.7 kg) were lost in the low-carb group, 6.4 pounds (2.9 kg) were lost in the low-fat group, and 9.7 pounds (4.4 kg) were lost in the mediterranean diet group.
Conclusion: The low-carb group lost more weight than the low-fat group, and the improvement in HDL (good) cholesterol and triglycerides was greater.
17. Keogh, JB, etc. Effects of very low carbohydrate diet weight loss on endothelial function and cardiovascular disease risk markers in abdominal obese subjects. Trusted Source American Journal of Clinical Nutrition, 2008.
details: in this study, 107 people with abdominal obesity followed a low-carb or low-fat diet for 8 weeks, all with calorie intake restricted.
Weight loss: the low-carb group lost 7.9% of its body weight, while the low-fat group lost 6.5%.
Conclusion: the low-carb group lost more weight. there were also no differences in common markers or risk factors between groups.
18. Tay, J. et al. In subjects with abdominal obesity, weight loss had a metabolic effect on an extremely low-carbohydrate diet compared to an equal-calorie high-carbohydrate diet. Journal of the American College of Cardiology, 2008.
details: 88 people with abdominal obesity followed a very low-carb or low-fat diet for 24 weeks. both diets limit calories.
Weight loss: people in the low-carb group lost an average of 26.2 pounds (11.9 kg), while those in the low-fat group lost an average of 22.3 pounds (10.1 kg). however, the difference was not statistically significant.
Conclusions: Both diets resulted in similar weight loss results and improvements in triglycerides, HDL (good) cholesterol, C-reactive protein, insulin, insulin sensitivity, and blood pressure. Total cholesterol and LDL (bad) cholesterol improved only in the low-fat group.
19. Volek, JS, etc. Carbohydrate restriction has a greater impact on metabolic syndrome than on a low-fat diet. Trusted Source Lipids, 2009.
Details: 40 people with cardiovascular risk factors followed a low-carb or low-fat diet for 12 weeks, both of which restricted calorie intake.
Weight loss: the low-carb group lost 22.3 pounds (10.1 kg) and the low-fat group lost 11.5 pounds (5.2 kg).
Conclusion: people in the low-carb group lost almost twice as much weight as the low-fat group, even though they had the same calorie intake.
furthermore:
- Triglycerides decreased by 107 mg/dL on low-carb diets, but only 36 mg/dL in low-fat diets.
- hdl (good) cholesterol increased by 4 mg/dl in a low-carb diet but decreased by 1 mg/dl in a low-fat diet.
- APOLIPOPROTEIN B DECREASED BY 11 POINTS IN A LOW-CARB DIET, BUT ONLY 2 POINTS IN A LOW-FAT DIET.
- ldl particle size increases in low-carb diets, but low-fat diets remain unchanged.
in a low-carb diet, the ldl granules are partly small to large, which is good. however, in a low-fat diet, they partially go from large to small, which is less healthy.
20. Brinkworth, GD, etc. After 12 months, the long-term effects of an extremely low-carb weight loss diet compared to an equal-calorie low-fat diet. Trusted Source American Journal of Clinical Nutrition, 2009.
Details: in this study, 118 people with abdominal obesity followed a low-carb or low-fat diet for 1 year. both diets limit calories.
Weight loss: People in the low-carb group lost 32 pounds (14.5 kilograms), while those in the low-fat group lost 25.3 pounds (11.5 kilograms). the difference was not statistically significant.
Conclusion: Compared with the low-fat group, the decrease in triglycerides was greater, and the increase in HDL (good) and LDL (bad) cholesterol was greater.
21. Hernandez, TL et al. Lack of inhibition of circulating free fatty acids and hypercholesterolemia during weight loss in a high-fat, low-carb diet. Trusted Source American Journal of Clinical Nutrition, 2010.
Details: 32 obese adults followed a low-carbohydrate or calorie-restricted, low-fat diet for 6 weeks.
Weight loss: the low-carb group lost 13.7 pounds (6.2 kilograms) and the low-fat group lost 13.2 pounds (6.0 kilograms). the difference was not statistically significant.
Conclusion: The decrease in triglycerides (43.6 mg/dL) in the low-carbohydrate group was greater than that in the low-fat group (26.9 mg/dL). In the low-fat group alone, both LDL (bad) and HDL (good) cholesterol declined.
22. Krebs, NF, etc. The effectiveness and safety of high-protein, low-carb diets for weight loss in severely obese adolescents. Journal of Trusted Source Pediatrics, 2010.
details: 46 individuals followed a low-carb or low-fat diet for 36 weeks. people in the low-fat group limit their calorie intake.
Weight loss: The Z-body mass index (BMI) decline was greater in the low-carbohydrate group compared to the low-fat group, but there was no difference in weight loss between groups.
Conclusions: The low-carbohydrate group had a greater reduction in BMI Z-score, but weight loss was similar between groups. Various biomarkers improved in both groups, but there were no significant differences between them.
23. Guldbrand H. et al. In type 2 diabetes, randomized recommendations to follow a low-carb diet temporarily improve blood sugar control compared to following the recommendations for a low-fat diet to produce similar weight loss. Diabetology, 2012.
Details: 61 people with type 2 diabetes followed a low-carbohydrate or low-fat diet for 2 years, both of which restricted calorie intake.
Weight loss: the low-carb group lost 6.8 pounds (3.1 kg) while the low-fat group lost 7.9 pounds (3.6 kg). the difference was not statistically significant.
Conclusion: there were no differences in weight loss or common risk factors between groups. the low-carb group had significant improvements in blood glucose control at 6 months. however, adherence is poor, and as people begin to consume more carbohydrates, the effect diminishes at 24 months.
Weight loss
the chart below shows weight loss between the 23 studies. in 21 studies, people lost weight.
most studies have found significant differences in weight loss in favor of low-carb diets.
furthermore:
- the low-carb group typically weighs 2-3 times as much as the low-fat group. in a few cases, there is no significant difference.
- for the most part, the low-fat group followed calorie restrictions, while the low-carb group consumed as many calories as needed.
- while both groups restricted calories, low-carb dieters still lost more weight (1, 2, 3), although it wasn't always important (4, 5, 6).
- in only one study, the low-fat group lost more weight (7), but the difference was small—1.1 pounds (0.5 kilograms)—and was not statistically significant.
- in several studies, weight loss was greatest at the outset. over time, people start to give up dieting and their weight begins to rebound.
- low-carb diets are more effective at reducing belly fat, which researchers have linked to a variety of health conditions. (8, 1, 3）。
there are two reasons why a low-carb diet is more effective at weight loss:
- at high protein content
- the effect of diet in suppressing appetite
these factors can help reduce a person's calorie intake.
LDL (bad) Cholesterol
low-carb diets usually do not raise total cholesterol and ldl (bad) cholesterol levels.
a low-fat diet can lower total cholesterol and ldl (bad) cholesterol, but this is usually only temporary. after 6-12 months, the difference is usually not statistically significant.
some healthcare providers report that a low-carb diet causes an increase in ldl (bad) cholesterol and other lipid markers in a small number of people.
however, the authors of the above study did not notice these adverse effects. studies looking at higher lipid markers (8, 3) showed only improvements.
HDL (Good) Cholesterol
One way to raise your levels of good cholesterol (HDL) is to eat more fat. For this reason, it is not surprising that low-carb (high-fat) diets are more likely to raise good cholesterol (HDL) than low-fat diets.
High (good) HDL levels may help improve metabolic health and reduce the risk of cardiovascular disease. HDL (good) levels are usually low in patients with metabolic syndrome.
Eighteen of the 23 studies reported changes in good cholesterol (HDL) levels.
Low-carb diets typically raise HDL (good) levels, but these levels appear to vary less on low-fat diets. In some cases, it decreases.
Triglycerides
Triglycerides are important cardiovascular risk factors and other key symptoms of metabolic syndrome.
the best way to lower triglycerides is to eat fewer carbohydrates, especially less sugar.
nineteen of the 23 studies reported changes in blood triglyceride levels.
both low-carb and low-fat diets help lower triglycerides, but the low-carb group is more effective.
Blood
sugar, insulin levels, and type ii diabetes
people without diabetes found that their blood sugar and insulin levels improved on both low-carb and low-fat diets. differences between groups are usually small.
three studies compared how diet affected people with type 2 diabetes.
only one study managed to adequately reduce carbohydrates.
In this study, various improvements were seen, including a sharp decline in HbA1c, a marker of blood sugar levels. (9）。 In addition, more than 90 percent of people in the low-carb group managed to reduce or eliminate their diabetes medications.
however, the differences were small or absent in the other two studies because of poor adherence. participants ended up consuming about 30 percent of their calories in the form of carbohydrates. (10, 7)。
Blood pressure
when measured, there was a downward trend in blood pressure in both diets.
How many people completed?
A common problem in weight loss research is that people often give up dieting before the study is complete.
Nineteen of the 23 studies reported on the number of people who completed the study.
The average percentage of people who follow a diet from start to finish is:
- low carbohydrate group: 79.51%.
- low-fat group: 77.72%.
this suggests that a low-carb diet is no more difficult to adhere to than other types of diets.
the reason may be that a low-carb diet seems to reduce hunger pangs (11, 12) and participants can eat until they are full. at the same time, low-fat diets usually limit calorie intake. the person needs to weigh their food and count calories, which can be onerous.
in a low-carb diet, individuals can also lose more weight and lose more faster. this may increase their motivation to continue eating.
Adverse effects
participants in these studies did not report any serious adverse reactions caused by any diet.
overall, a low-carb diet appears to be well tolerated and safe.
Bottom line
Many people traditionally choose a low-fat diet and count calories to lose weight.
however, the results of these studies suggest that a low-carb diet may be as effective as, or even more effective, than a low-fat diet.