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Low Carb High Fat - The Effect on Weight Loss, Diabetes, and Metabolic Risk Factors Compared to Other Diets

Low-Carb High-Fat - The Effect on Weight Loss, Diabetes, and Metabolic Risk Factors Compared to Other Diets



Low-carbohydrate and high-fat (LCHF) diets are increasing in popularity as new research continues to emerge disproving the the merits of the low-fat dogma that has shaped Australian dietary guidelines and those of most of the western world since the 1960s. The counterargument has been packaged in various forms like paleo, primal, ancestral and keto. As we rediscover these traditional ideas of food consumption, so too are we seeing the resurgence of a healthy population.


Low-carbohydrate diets have gained increased attention in recent years. Dr. Robert Atkins, a cardiologist, was one of the first to prominently promote a low-carbohydrate, high-fat (LCHF) diet as opposed to the low-fat diet propagated by the nutritional guidelines of most Western countries.

Atkins was ridiculed at a time when carbohydrates were the foundation of America’s Food Guide Pyramid following the claims of an American scientist called Ancel Keys. Keys studied the association between cardiovascular disease and diet in seven different countries. He concluded that those countries with the highest fat consumption also had the highest incidence of heart disease.

Although this study was later proven flawed because Keys only chose those countries that supported his hypothesis, it had a big influence on American dietary guidelines, which was then echoed throughout the world. The flavourful fat in many products had to be replaced by something else to make the stripped down foods palatable. The answer was sugar or high fructose corn syrup. The result was that the consumption of refined carbohydrates increased exponentially. But instead of becoming healthier, the incidence of obesity and type 2 diabetes among the general population increased at the same time.

Low carb high fat diets were not popular when obesity epidemic happened

This graph from the US National Center of Health Statistics shows the obesity epidemic started at almost the same time the low-fat dietary guidelines came into effect. More recently, prof. Tim Noakes from South Africa has drawn a large international following with his Real Meal Revolution to “correct the dietary errors of the past fifty years.” The Noakes Foundation was set up to support what it calls “the dietary revolution that will reverse the global epidemics of obesity and type 2 diabetes mellitus.” It aims to advance medical science’s understanding of the benefits of a LCHF diet through evidence-based information. The foundation currently has six research projects underway. This includes a study on carbohydrate restriction and high-fat diets to improve insulin resistance, weight loss, health and reverse/improve type 2 diabetes.

Several studies in the US and other countries have already successfully challenged the low-fat dietary approach. In the past 13 years, more than 20 comparative studies were done on the effects of a low-carbohydrate diet versus a low-fat diet. In other studies, a low-carbohydrate diet was compared to a low-glycaemic diet.

Most of the studies focus on weight loss, type 2 diabetes and metabolic risk factors. Apart from weight loss, they typically measure blood sugar levels, total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides. With obesity, diabetes and metabolic syndrome counting among the biggest health problems in the world, this comes as no surprise.

An analysis of the research is only helpful if we have a general understanding of what the different diets are about.

Concentrates on eating fewer carbohydrates and a higher proportion of fat. Restricts the intake of sugar and starches. The consumption of most vegetables, certain fruits and nuts, meat, seafood, and dairy with a high fat content is allowed. Roughly consists of 60% fat, 30% protein, and 10% carbohydrate.

High in fat, including saturated fat, adequate in protein, and low in carbohydrate. Roughly based on 75% fat, 20% protein, and 5% carbohydrate.

Reduces dietary fat and emphasizes whole grain products and a variety of fruits and vegetables. Promotes the consumption of unsaturated plant-based fats. Roughly consists of 60% carbohydrates, 20% protein and 20% fat.

Focus on carbohydrates low on glyceamic index (GI), which ranks foods based on their immediate effect on blood sugar levels. Includes non-starchy vegetables, wholegrains, lean proteins and unsaturated plant-based fats. Roughly based on 40% carbohydrates, 40% fat and 20% protein.

Promotes daily consumption of 70% plant foods, including vegetables, fruit and grains. The remaining 30% is made up largely by low-fat dairy, lean meat, eggs, nuts, seeds, and legumes, with plant-based unsaturated fats at the top. National Dietary guidelines continue to neglect entering the conversation around food sources like organics and pasture-raised meats.

Major Studies and Their Findings:

LCHF Diet Effects on Weight Loss

Which combination of carbohydrate, fat and protein is best for people trying to achieve and maintain weight loss? This is the question more and more scientists have been wanting to answer.

In 2012, researchers from the Children’s Hospital Boston and Brigham and Women’s Hospital, Boston, examined the effects of three diets – low-fat, low-glycaemic and very low-carbohydrate – on energy expenditure following weight loss. Published in the Journal of the American Medical Association, they found that those diets that reduced the surge in blood sugar after a meal – low-glycaemic and very low-carbohydrate – are more effective in achieving lasting weight loss. The study concluded that “a strategy to reduce glycemic load rather than dietary fat may be advantageous for weight-loss maintenance…”

In one of the most comprehensive studies called "Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial," researchers found that a low-carbohydrate diet was more effective for weight loss than a low-fat diet. The 148 participants in the study that was published in 2014 followed either a low-carbohydrate diet (less than 40g of carbohydrates per day) or a low-fat diet for an entire year. Those on the low-carbohydrate diet lost three times more weight as well as more fat mass.

Addressing the concerns of obese people seeking to lose weight but who are cautious about the effect of the high-fat content of a LCHF diet on their arterial health, researchers at Johns Hopkins University concluded that “a low-carb approach does not seem to pose any immediate risk to vascular health.”

The 2011 study followed the weight loss of 46 men and women, weighing 218 pounds on average. One half followed a LCHF diet and the other half a low-fat diet. The LCHF dieters dropped 10 pounds in 45 days, while the low-fat group took on average 70 days, nearly a month longer, to lose the same amount of weight. Furthermore, the LCHF dieters showed no harmful vascular changes.

“Our study should help allay the concerns that many people who need to lose weight have about choosing a low-carb diet instead of a low-fat one, and provide re-assurance that both types of diet are effective at weight loss and that a low-carb approach does not seem to pose any immediate risk to vascular health." - prof. Kerry Stewart, director of clinical and research exercise physiology at the Johns Hopkins University School of Medicine and its Heart and Vascular Institute.

In an analysis of 23 studies comparing low-carbohydrate and low-fat diets, Kris Gunnars from AuthorityNutrition concluded that the low-carbohydrate groups often lost 2-3 times as much weight as the low-fat groups. Only in a few instances, there was no significant difference.

Low-carb and low-fat diets with weight loss

Graph published in AuthorityNutrition.com, showing the difference in weight loss in 21 studies comparing low-carbohydrate and low-fat diets.

LCHF Diet Effects on Type 2 Diabetes

The number of people with type 2 diabetes has risen from 108 million in 1980 to 422 million in 2014, according to the World Health Organisation (WHO). Type 2 diabetes is the most common form of diabetes and is characterized by elevated blood sugar levels due to insulin resistance. The number of people with prediabetes or borderline diabetes, the precursor to type 2 diabetes, has risen accordingly. In England alone, one in three adults have prediabetes, according to an analysis of the Health Survey for England for the years 2003, 2006, 2009 and 2011. Statistics from Diabetes Australia show 280 people develop diabetes every day, with 1.7 million Australians already suffering from the disease.

Several studies have been dedicated to comparing a diet low in carbohydrates to one focusing on carbohydrates with a low glycemic index to determine which works better at controlling type 2 diabetes.

A study performed at Duke University and published in the online journal Nutrition and Metabolism found that a diet low in carbohydrates and with the lowest possible rating on the glycemic index leads to greater improvement in blood sugar control.

Dr. Eric Westman, Director of Duke’s Lifestyle Medicine Programme, commented on the results as follows: “Low-glycemic diets are good, but our work shows a no-glycaemic diet is even better at improving blood sugar control. We found you can get a three-fold improvement in type 2 diabetes as evidenced by a standard test of the amount of sugar in the blood.”

This finding corresponds with a 2014 study titled "Clinical Application of the Food Insulin Index to Diabetes Mellitus" by Kirstine Bell from the University of Sydney. A food’s insulin index represents the extent to which its consumption elevates the insulin concentration of the blood in the two hours after the food was eaten. The insulin index is similar to the glycemic index, but measures blood insulin levels rather than blood glucose levels. Bell found that type 2 diabetics managed to improve their blood sugar control by eating foods that caused a lower insulin secretion. They chose the foods independent of calories or carbohydrates.

Another study published in the Annals of Internal Medicine sought to determine the effect of a low-carbohydrate diet on appetite, blood glucose levels, and insulin in obese patients with type 2 diabetes. The study observed 10 patients with type 2 diabetes during seven days of a usual diet and 14 days of a low-carbohydrate diet (21g of carbohydrates per day). It found that the low-carbohydrate diet resulted in spontaneous reduction in energy intake to a height appropriate level. Weight loss accounted for by reduced caloric intake was recorded, as well as improved 24-hour blood glucose profiles, insulin sensitivity, and haemoglobin A1c.

LCHF Diet Effects on Metabolic Risk Factors

Globally, Cardiometabolic Disease (CMD), which includes cardiovascular disease and type 2 diabetes, is a leading cause of mortality. In the Middle East and North Africa alone it accounts for nearly one million deaths annually.

Several studies have been done to determine how various risk factors contribute to CMD. The WHO identifies four metabolic factors (high blood cholesterol, high blood pressure, high blood glucose and adiposity) and one dietary factor (too little vegetables and fruits combined) among multiple risk factors that contribute to disease. Other metabolic risk factors include triglycerides, total cholesterol, ratio of total to HDL cholesterol, serum insulin, and fasting blood glucose.

The effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors were compared in a meta-analysis of randomised controlled trials published in the American Journal of Epidemiology in 2012. It found several studies which showed significant changes in metabolic risk factors associated with low-carbohydrate diets.

The researchers remarked that there was a substantial body of evidence to suggest that both low-carbohydrate diets and low-fat diets reduced blood pressure, total to HDL cholesterol, total cholesterol, LDL cholesterol, blood glucose, serum insulin levels, and triglycerides. Participants on low-carbohydrate diets had bigger decreases in triglycerides and greater increases in HDL cholesterol, but lesser decreases in total and LDL cholesterol.

Despite the small differences, it was found that “low-carbohydrate diets had beneficial effects on weight loss and metabolic risk factors, and these effects are comparable to those seen on low-fat diets.” On these grounds, it was suggested that dietary recommendations for weight loss should be revisited to consider additional evidence of the benefits of low-carbohydrate diets.


A substantial body of research exists that shows the effectiveness of low-carbohydrate diets in weight management, the prevention and treatment of prediabetes and type 2 diabetes, and on metabolic risk factors.

This evidence has not been enough to influence the health authorities of most Western countries to revise their dietary guidelines, despite the WHO’s recommendation in 2015 that adults and children reduce their daily intake of free sugars to less than 10% of their total energy intake.

The American Heart Association and the National Institutes of Health still emphasises the importance of diets low in fat and high in carbohydrates. In the UK, the National Obesity Forum and the Public Health Collaboration, accused the major public health bodies of colluding with the food industry. It called for a “major overhaul” of the current dietary guidelines because the low-fat approach was failing to resolve Britain’s obesity crisis.

Sweden is the only country where the health authorities made changes to their official recommendations after studying research on the effects of a low-carbohydrate diet. They agreed that a LCHF diet might be beneficial for people wanting to lose weight and with type 2 diabetes.

For these changes to take effect everywhere, more research and meta-analysis comparing the effects of low-carbohydrate diets with other diets is timely and important. The results of The Noakes Foundation’s studies are keenly awaited. Another study to keep an eye on (follow its progress here: http://nusi.org/science-in-progress/stanford-university/) is a 4-year comparison of the effects of low-carbohydrate and low-fat diets on the weight loss of 600 overweight and obese patients, ending in December 2016. What makes this study important, is that the participants come from different genetic and clinical backgrounds. It should, for the first time ever, be able to document the changes in free-living participants when following either a very low-carbohydrate or very low-fat diet.



Afshin A, et al. The impact of dietary habits and metabolic risk factors on cardiovascular and diabetes mortality in countries of the Middle East and North Africa in 2010: a comparative risk assessment analysis. BMJ Open 2015;5:e006385 doi:10.1136/bmjopen-2014-006385

Bazzano LA, Hu T, Reynolds K, Yao L, Bunol C, Liu Y, Chen CS, Klag MJ, Whelton PK, He J. (2014). Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial. Annals of Internal Medicine. 2014;161 (5):309-318. DOI: 10.7326/M14-0180.

Bell, Kirstine. Clinical Application of the Food Insulin Index to Diabetes Mellitus. (2014). Retrieved from http://hdl.handle.net/2123/11945

Diabetes in Australia. (2016). Diabetes Australia. Retrieved from https://www.diabetesaustralia.com.au/diabetes-in-australia

Ebbeling CB, Swain JF, Feldman HA, Wong WW, Hachey DL, Garcia-Lago E, Ludwig DS. Effects of Dietary Composition on Energy Expenditure During Weight Loss Maintenance. Journal of American Medicine. doi:10.1001/jama.2012.6607. Retrieved from http://jamanetwork.com/journals/jama/fullarticle/1199154

Gunnars, Kris. 23 Studies on Low-Carb and Low-Fat Diets – Time to Retire The Fad. AuthorityNutrition. Retrieved from https://authoritynutrition.com/23-studies-on-low-carb-and-low-fat-diets/

Gunnars, Kris. Modern Nutrition Policy is Based on Bad Science. Retrieved from https://authoritynutrition.com/modern-nutrition-policy-lies-bad-science/

Hu, T., Mills, K. T., Yao, L., Demanelis, K., Eloustaz, M., Yancy, W. S., … Bazzano, L. A. (2012). Effects of Low-Carbohydrate Diets Versus Low-Fat Diets on Metabolic Risk Factors: A Meta-Analysis of Randomized Controlled Clinical Trials. American Journal of Epidemiology176(Suppl 7), S44–S54. http://doi.org/10.1093/aje/kws264

Insulin index. Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Insulin_index

Low-carb, high-fat diets add no arterial health risks to obese. (2011, August 1). The JHU Gazette. Retrieved from http://archive.gazette.jhu.edu/2011/08/01/low-carb-high-fat-diets-add-no-arterial-health-risks-to-obese/

One in three adults in England ‘has prediabetes’. (2014, June 10). NHS. Retrieved from http://www.nhs.uk/news/2014/06June/Pages/One-in-three-adults-in-England-has-prediabetes.aspx

The Noakes Foundation. http://www.thenoakesfoundation.org/

WHO calls on countries to reduce sugars intake among adults and children. (2015, March 4). World Health Organisation. Retrieved from http://www.who.int/mediacentre/news/releases/2015/sugar-guideline/en/

World Health Organisation. Type 2 Diabetes. Retrieved from http://www.who.int/mediacentre/factsheets/fs312/en/

Linda de Beer
Linda de Beer