Low Carb and Low Fat Diets: 27 Reviewed Studies (Updated)

When it comes to treating diabetes, obesity and epilepsy, low carb diets have been used for many years as a therapeutic tool.

Millions of people have been very successful with it.

In spite of all of this, a few stubborn nutritionists and other health experts do not recommend a low carb diet citing that it can be too dangerous and unhealthy in the long run.

Many claim the scientific evidence behind low carb diets is insufficient and refer to them as a ‘fad’ diet.

In this article, I will prove them wrong.

Ten years ago, there was not much scientific evidence behind the low-carbohydrate diet, however since 2003, there have been over 27 randomized, controlled, scientific human trials.

Randomized controlled trials are the gold standard in the public health and medical science community that prove safety, cause and effect.

In this article, I will review 27 trials that were published in the New England Journal of Medicine, American Journal of Clinical Nutrition and Nature (2003-2016)

Over the years, I have asked Nutritionists and other health experts who are against low-carb diets to prove they are ineffective or unsafe.  The fact is – such trials do not exist.

All of the randomized controlled trials compare the low-carb diet to the standard, calorie-restricted, low-fat diet that is often recommended by many health professionals.

There is no one diet plan that is perfect for everyone.

The best eating plan is one with lifestyle habits and changes that can be easily followed by an individual for life.

My goal is for the media, general public and health professionals to acknowledge low-carb diets as a viable option for those dealing with obesity, diabetes, and symptoms of metabolic syndrome – a condition that is becoming quite prevalent throughout the world.

All the scientific evidence suggests that a low carb diet is easier, healthier and more effective than a calorie-restricted, low-fat diet that is often recommended by health professionals.

Studies on Low-Carb Low-Fat Diets (In Chronological Order)

1. 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: In 2003, the Journal of Pediatrics conducted a 12-week study to determine the effects of a low-carbohydrate diet on overweight, adolescent individuals with risk factors for cardiovascular disease.

The study consisted of 30 individuals who were randomly placed in a either a low-carbohydrate or low-fat group without restriction of calories.

Results Of The Study: The low-carbohydrate group lost an average of 21.8 pounds while the low-fat group lost an average of 9 pounds. Plus, the low-carbohydrate group had significant improvements in their triglyceride and cholesterol levels.

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: In 2003, the New England Journal of Medicine conducted another study that lasted six months with 132 individuals who had an average BMI of 43 and were considered severely obese. Most of the subjects had Type 2 diabetes and metabolic syndrome.

Study results: The low-carbohydrate group lost an average of 12.8 pounds while the low-fat group lost only 4.2 pounds. Most individuals saw a significant improvement in triglyceride and cholesterol level.

Recommended Reading: Intermittent Fasting on the Keto Diet Plan – Is it Good?

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

Details: In 2003, the New England Journal of Medicine conducted a study that lasted for one year and randomly placed 63 individuals in either a low-carbohydrate or a low-fat group with calorie restrictions.

Results Of The Study: The low-carbohydrate group lost 7.3% of total body weight compared to the low-fat group who only lost 4.5% of their total body weight.

Details: In 2003, The Journal of Endocrinology and Metabolism conducted a randomized trial that compared a low-carbohydrate diet and a calorie-restricted, low-fat diet in healthy women.

The study looked at cardiovascular risk factors as well as body weight.

The study lasted six months and included 53 obese women who were randomly placed in.

Results Of The Study: The low-carbohydrate group lost an average of 18.7 pounds while the low-fat group lost an average of 8.6 pounds.

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 participants were randomized to either a modified low-carb diet or a low-fat diet based on the National Cholesterol Education Program. Both groups are calorie restricted.

Weight Loss: The modified low-carb group lost an average of 13.6lb (6.2kg) while the low-fat group lost an average of 6.1lb (2.8kg).

Cardiac Risk Factors: There were no significant differences in blood lipids between groups. The modified low-carb group decreased total cholesterol, triglycerides, and percentage of dense LDL while increasing LDL particle size. The low-fat group decreased total, HDL and LDL cholesterol.

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: There were 119 obese, hyperlipidemic individuals randomly assigned to either a low-carbohydrate, ketogenic diet or a low-fat diet group.  Calories were restricted in the low-fat group.

Weight Loss Results: The group on the low-carb diet lost an average of 12.0 kg or 24.0 pounds, while the low-fat group lost an average of 6.5 kg or 13.0 pounds.

Results Of The Study: Those on the low-carb diet experienced decreased triglycerides while HDL cholesterol levels increased.

The group on the low-fat diet experienced a lowering of total cholesterol and decreased triglycerides.

In fact, there was a significant difference between the groups when measuring for triglycerides and HDL levels, that prove the low-carb diet was successful.

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 Of The Study: There were 28 overweight men and women randomly assigned to eat a calorie-restricted, low-carb diet or a calorie-restricted low-fat diet.  The low-carb group ate 300 more calories per day.

The outcomes measured included weight loss, body composition, trunk fat mas and resting energy expenditures for both groups.

Weight Loss: In spite of eating more calories per day, the low-carb group lost more weight than the low-fat group.

Naturally, the men lost more weight than the women. The ratio of trunk fat and total fat also decreased for those on the low-carb diet, meaning they lost more abdominal fat, the most dangerous kind of body fat.

Results Of The Study: For those on the low-carb diet, resting energy expenditure did not decrease, however, it did decrease for those on the low-fat diet.

The loss of fat in the trunk or abdominal region was three times greater for those on the low-carb diet compared to those on the 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 and obese men and women randomized to either a low-carb or a low-fat diet. The calories in the low-fat group were matched to the calories in the LC group, although the LF group eventually ate a bit less. Study went on for 10 weeks.

Weight Loss: Both groups lost a similar amount of weight. LC lost 7.0kg and the LF group lost 6.8kg. No statistically significant difference.

Risk Factors: Total and LDL cholesterol remained unchanged in the LC group but decreased in the LF group. HDL decreased in the LF group and increased in the LC group. Both groups lowered their triglyceride levels.

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/obese premenopausal women were placed on either a low-carb/high-protein or a high-carb/low-fat diet for 6 weeks. Primary outcomes measured were hunger and cognitive eating restraint. High-carb/low-fat group was calorie restricted.

Weight Loss: The women on the low-carb/high protein diet lost more weight (5.7% of body weight) compared to the high-carb/low-fat group (3.3% of body weight).

Outcomes Measured: The LC/HF group of women had less hunger than the HC/LF group, but both groups exhibited similar cognitive eating restraint (CER).

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

Details: 102 type II diabetics randomized to either a low-carb or a low-fat diet. Study went on for three months. Main outcomes measured were weight, glycaemic control, lipids and blood pressure. The low-fat group was instructed to reduce portion sizes.

Weight Loss: The LC group lost more weight, -3.55kg, while the LF group lost 0.92kg.

Other Outcomes Measured: The ratio of Total cholesterol:HDL improved on the LC group. Triglycerides, Systolic blood pressure and HbA1c (a marker for blood glucose levels) also decreased on the LC diet, but the difference was not statistically significant compared to the low-fat diet.

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 individuals randomized to either a low-carb, ketogenic diet or a calorie restricted low-fat diet for 6 months. Main outcomes measured are mood, hunger and other self reported symptoms.

Weight Loss: The LC group lost 12.9kg, while the LF group lost 6.7kg.

Other Outcomes Measured: The LC group had significantly better mood (less negative affect) and less hunger than the LF group.

Christopher D. Gardner, PhD; Alexandre Kiazand, MD; Sofiya Alhassan, PhD; Soowon Kim, PhD; Randall S. Stafford, MD, PhD; Raymond R. Balise, PhD; Helena C. Kraemer, PhD; Abby C. King, PhD – JAMA. 2007;297(9):969-977

Details: 311 overweight/obese premenopausal women assigned to either an Atkins, Zone, LEARN or Ornish diet for 12 months. Zone and LEARN were calorie restricted, Atkins and Ornish were not.

Weight Loss: Weight loss was greatest at 12 months in the Atkins group (-4.7Kg) compared to the LEARN (-2.6Kg), Zone (-1.6Kg) and Ornish group (-2.2kg).

Risk Factors: Triglycerides decreased and HDL increased on the Atkins diet. LDL cholesterol favoured the LEARN and Ornish (low-fat) groups at 2 months, but the effects dimished at 6 and 12 months. Systolic blood pressure was significantly lower in the Atkins group at 12 months compared to the other groups, and diastolic blood pressure significantly lower than the Ornish (very low fat) group.

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: A low-carb diet compared to a low-fat diet in 93 overweight or obese individuals for 8 weeks. Outcomes measured were weight loss, mood and cognitive function. Both groups were calorie restricted.

Weight Loss: The LC group lost more weight, 7.8kg, compared to the LF group which lost 6.4kg.

Other Outcomes: Both LC and LF groups had significant improvements in mood, with no difference between groups. Both groups improved cognitive function. Speed of processing improved less in the LC group.

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.
P. A. Dyson, S. Beatty and D. R. Matthews – Diabet. Med. 24, 1430–1435 (2007)

Details: Over a period of three months, 13 diabetic and 13 non-diabetic individuals were assigned to either a low-carb or a low-fat diet with caloric restrictions.

The measurements included body weight, glycated hemoglobin (HbA1c), ketone and lipid levels.

Weight Loss: The LC group lost 6.9kg while the low-fat group lost 2.1kg.

Other Outcomes Measured: There was no statistically significant difference in any of the other parameters.

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: 322 moderately obese individuals randomized to either a low-fat calorie restricted diet, a mediterranean calorie restricted diet or a low-carb non-restricted diet for 2 years.

Weight Loss: The LF group lost 2.9kg, the mediterranean group lost 4.4kg and the LC group lost 4.7kg.

Risk Factors: The LC group improved both HDL and Triglycerides, and the ratio of Total:HDL cholesterol, compared to the other groups.

16. Shai I, et al. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. New England Journal of Medicine, 2008.

Details: 84 obese and type II diabetic individuals randomized to either a low-carb ketogenic diet or a low glycemic index calorie-restricted diet for 3 months.

Weight Loss: The LC group lost 11.1kg and the LF group lost 6.9kg.

Other Outcomes Measured: The LC group had more improvements in HbA1c and High-Density Lipoprotein. Diabetes medication were reduced or eliminated in 95.2% of the LC group, compared with 62% of the low glycemic index diet.

17. Keogh JB, et al. Effects of weight loss from a very-low-carbohydrate diet on endothelial function and markers of cardiovascular disease risk in subjects with abdominal obesity. American Journal of Clinical Nutrition, 2008.

Details: 107 individuals randomized to either a very low-carbohydrate diet or a low-fat diet for 8 weeks. Both groups were calorie restricted. Main outcomes measured were markers of endothelial function and cardiovascular disease risk.

Weight Loss: The LC group lost more weight, 7.5kg, compared to the LF group which lost an average of 6.2kg.

Risk Factors: There was no difference between groups on endothelial function. The LC group had further improvements in Triglycerides and HDL, compared to the low-fat group.

18. Tay J, et al. Metabolic effects of weight loss on a very-low-carbohydrate diet compared with an isocaloric high-carbohydrate diet in abdominally obese subjects. Journal of The American College of Cardiology, 2008.

Details: 88 obese individuals randomized to either a low-carb, high-fat diet or a high-carb, low-fat diet for 6 months. Both groups were calorie restricted. Main outcomes measured were weight loss and cardiac risk factors.

Weight Loss: The LC group lost 11.9kg and the LF group lost 10.1kg. The difference between groups was not statistically significant.

Cardiac Risk Factors: Triglycerides and HDL improved further in the LC group, while Total and LDL cholesterol improved in the LF group. 24% of individuals on the low-carb diet increased LDL cholesterol by 10% or more.

19. Volek JS, et al. Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet. Lipids, 2009.

Details: 40 subjects with atherogenic dyslipidemia randomized to either a low-carb or an isocaloric low-fat diet for 12 weeks. Main outcomes measured were markers of the metabolic syndrome.

Weight Loss: Despite a similar reduction in calories, the low-carb group lost double the amount of weight as the low-fat group (10.1kg vs. 5.2kg).

Risk Factors: The LC group showed more favourable improvements in triglycerides, HDL, Triglyceride:HDL ratio. The LC group also had more improvements in fasting glucose, fasting insulin and a reduction in small LDL particles.

20. Brinkworth GD, et al. Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 months. American Journal of Clinical Nutrition, 2009.

Grant D Brinkworth, Manny Noakes, Jonathan D Buckley, Jennifer B Keogh, and Peter M Clifton – Am J Clin Nutr 2009;90:23–32.

Details: 118 obese individuals randomized to either a low-carb or a low-fat diet for 12 months. Both groups were calorie restricted.

Weight Loss: The LC group lost 14.5kg of weight, while the LF group lost 11.5. The difference was not statistically significant.

Risk Factors: Compared to the LF group, the LC group increased HDL, Total and LDL cholesterol and decreased triglycerides.

21. Hernandez, et al. Lack of suppression of circulating free fatty acids and hypercholesterolemia during weight loss on a high-fat, low-carbohydrate diet. American Journal of Clinical Nutrition, 2010.

Details: 32 obese adults were randomized to a low-carb or a calorie restricted, low-fat diet for 6 weeks.

Weight Loss: The low-carb group lost 6.2 kg (13.7 lbs) while the low-fat group lost 6.0 kg (13.2 lbs). The difference was not statistically significant.

Conclusion: The low-carb group had greater decreases in triglycerides (43.6 mg/dL) than the low-fat group (26.9 mg/dL). Both LDL and HDL decreased in the low-fat group only.

22. Krebs NF, et al. Efficacy and safety of a high protein, low carbohydrate diet for weight loss in severely obese adolescents. Journal of Pediatrics, 2010.

Nancy F. Krebs, MD, MS, Dexiang Gao, PhD, Jane Gralla, PhD, Juliet S. Collins, MD, and Susan L. Johnson, PhD – J Pediatr 2010;157:252-8.

Details: 46 severely obese adolescents randomized to either a low-carb, high-protein diet or a calorie-restricted low-fat diet for 13 weeks.

Weight Loss: The LCHP group lost significantly more weight and had a significant reduction in the BMI-z score compared to the LF group.

Risk Factors: Both groups improved Total cholesterol and LDL cholesterol levels. HDL levels decreased in the LF group, while Triglycerides decreased in the LC group.

A clinical study published in Diabetoligia showed those who have type 2 diabetes have success in controlling blood sugar levels more successfully with a low-carbohydrate diet as opposed to following a low-fat diet.  (Diabetoliga, 2012)

Also read: Sugar Addition […and How To Break It!]

Details: The study included 61 people who had type 2 diabetes randomly chose a either a low-carbohydrate or low-fat eating plan and agreed to follow it for two years with restrictions in calories.

The results were amazing.  Individuals who followed a low-carbohydrate plan lost twice as much weight (on average 6.8 pounds) as those who followed a low-fat diet (average 7.9 pounds), however statistically, the difference was not significant.

24.A systematic review: Impact of dietary macronutrient distribution on BMI and cardiometabolic outcomes in overweight and obese children and adolescents: , Oxford Journals, 2014.

A Systematic Review was completed in 2012 that looked at macro-nutrient diet and their effect of percentages of protein, fats, and carbohydrates instead of calories alone on obese children and adolescents.

The objective of the study is to determine the effect on metabolism in overweight children and adolescents when placed on a ketogenic diet that high protein and fat diet with about 50 grams of carbohydrates per day and hypocaloric diet in which individuals simply eat less calories than what they burn.

The two different diets were implementd on 58 individuals (both children and adolescents) for a period of six months.

The method for measuring results included measuring height, weight, skin-fold thickness and circumference of the waist, hips and chest.  A lipid profile that is a panel of blood tests that measures cholesterol and triglyceride levels is also completed.

Before and after each diet, an assessment is done to determine if an individual is experiencing insulin resistance.

Both children and adolescents lost weight, inches and improved insulin levels, however those on the ketogenic diet experienced the greatest improvements.  Both groups increased their Whole Body Insulin Sensitivity Index (WBISI) considerably, however those on the ketogenic diet increased their high-molecular weight adiponectin (HMW), a fat-burning hormone.

Children experienced greater weight loss on a ketogenic diet and is proven to be a safe alternative for signficant improvement in all metabolic factors related to weight loss.

25.The Annals Of Internal Medicine (2014) published a study that focused on the effects of low-carbohydrate and low-fat diets, a randomized trial. 

The objective of the study was to test and compare the cardiovascular risk factors and body weight on a low-carbohydrate diet verses a low-fat diet.

Both men and women in the study (148 in total) did not have diabetes or clinical cardiovascular disease.

At the end of the study, 82% of those in the low-fat group and 79% of the low-carbohydrate group completed their program.  Those on the low-carbohydrate diet lost more weight and body fat than those on the low-fat diet.

Weight loss results: those on the low-carbohydrate diet experienced a greater reduction in weight and improved cardiovascular risk factors than the low-fat diet participants.

Eating a low-carbohydrate diet is an effective way to lose weight and improve health.

Information was tracked through 17 trials with 1,797 patients over a one-year period comparing low-carbohydrate and low-fat diets.

Those who consumed a low-carbohydrate diet experienced greater weight loss than those on strictly a low-fat diet.  Plus, those on the low-carbohydrate diet signiticantly reduced their risk factors for cardiovascular disease.

27. British Journal of Nutrition: Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials – 2016

The Atkins diet was used in the study featuring low-carbohydrate consumption of less than 20% of total caloric intake per day for at least six months or longer in healthy individuals.

Those on the low-carbohydrate diet (Atkins diet) experienced more weight loss compared to those on the low-fat diet.

In conclusion, cardiovascular risk factors were significantly reduced in those on the low-carbohydrate diet that included significant weight loss, however LDL cholesterol levels increased.

The Studies

I went through all of the studies (2003-2016), took me about 2 weeks.

Weight Loss on Low-Carb vs. Low-Fat Diets

Weight loss is, almost without exceptions, greater on low-carb diets although the difference isn’t always statistically significant.

This effect is especially evident when the low-carb group is allowed to eat until fullness while the low-fat group is calorie restricted, which is how these diets are usually prescribed in practice.

When both groups eat the same amount of calories (isocaloric), the low-carb groups still tend to lose more weight but the effects aren’t large enough to reach statistical significance.

Part of the reason for greater weight loss on the low-carb diet given that calories stay the same may be increased water loss.

Calories, Carbs, Fats and Protein

When the low-carb group is not calorie restricted but the low-fat group is, they tend to end up eating a similar amount of calories. Interestingly, calorie restricted low-fat dieters also end up eating a lower total amount of carbohydrates.

Another interesting observation is that on a low-carb diet, people don’t necessarily end up eating more fat than they used to. In fact, they tend to eat similar amounts of fat as they were before starting the diet.

Protein intake is higher on the low-carb diet, which may explain some of the increased satiety.

Appetite And Hunger

Low-carb diets tend to decrease appetite and hunger.

This is the main reason people lose so much weight without portion control or calorie restriction, they simply don’t want to eat as much.

Compliance and Attrition Rates

The studies where the LC diets are most effective are where people manage to follow them completely and restrict carbohydrates accordingly.

However, as with every weight loss diet, compliance is an issue and people tend to increase their carb intake over time. As carb intake increases, weight loss tends to slow down and some people even start gaining weight back.

This implies that weight loss on a LC diet (as with any diet, really) requires people to stick with it for life.

Attrition rates tend to be lower on LC diets (more people make it to the end) despite arguments by dietitians about LC diets being harder to stick to because they eliminate entire food groups.

This is probably due to the fact that people can eat until fullness and don’t have to be hungry all the time, which is common with calorie-restricted low-fat diets

The idea that low-carb diets are harder to follow is a myth!

LDL and Total Cholesterol levels

Low-fat diets tend to decrease both Total and LDL cholesterol, but mostly in the first 3 months or so. Then they tend to go back up.

It is not true that low-carb diets raise LDL or Total cholesterol levels. The fact is that they remain pretty much the same. They don’t get any higher than before, although there is some individual variation here.

This is probably nothing to worry about, as low-carb diets tend to change the LDL pattern from small, dense LDL to large, fluffy LDL which is benign.

HDL Cholesterol levels

HDL cholesterol (the “good” cholesterol) usually goes up substantially on a low-carb diet, while it tends to increase less or even go down on a low-fat, high-carb diet.

Blood Triglycerides

Blood triglycerides always go down on low-carb diets, while they tend to decrease less, stay the same or go up on calorie-restricted low-fat diets.

Blood Pressure

Blood pressure seems to decrease for both low-carb and low-fat dieters and the difference usually isn’t significant between groups.

Glucose, Insulin and Type II Diabetes

Glucose and insulin tend to decrease further on low-carb diets in non-diabetics, but it is not always statistically significant.

In type II diabetics, glucose and insulin levels decrease much more on low-carb diets and the patients are often able to eliminate or drastically reduce medication.

This implies that these diets may be particularly useful for those with diabetes or impaired glycemic control.

Adverse Effects

There were some mild side effects for those on the low-carb, ketogenic diets that usually last only a few days.  Some experienced headache, nausea, fatigue, insomnia and constipation.

However, there were no serious side effects from eating a low-carb, ketogenic diet, in spite of some of the scare tactics and/or misinformation.

It Is Time To Dispel The Myths

When it comes to weight loss, low-carb, ketogenic diets work more effectively than low-fat diets.  In addition to weight loss, they help reduce the major risk factors of many diseases including diabetes and heart disease.

The studies prove that low-carb diets are healthier and far superior compared to low-fat diets.  The low-carb diet is especially effective for those with diabetes, metabolic syndrome and obesity.

More weight loss can be achieved with a low-carb diet as opposed to low-fat, calorie-restricted diets, without being hungry.  Let’s face it – being hungry all the time is not a way to live.

Triglycerides, HDL and LDL cholesterol levels all improved for those on the low-carb diet, further reducing their risk for disease compared to those on the low-fat diets.

The most effective way to lose weight and reverse metabolic disease is through a healthy, low-carb diet.  The science behind this statements proves it.

It is time to dispel the myth about low-fat diets, once and for all.