Several studies have been published comparing low-carbohydrate, ketogenic diets with low-fat diets, mostly regarding the treatment of diabetes in overweight and obese participants. Prominent researchers in this field are Richard Feinman, Stephen Phinney, Mary Vernon, Jeff Volek, Eric Westman, and William Yancy—all supporters of low-carbohydrate dietary regimes.
In most of these studies, both low-carbohydrate diet and the low-fat control diet are calorie-restricted diets. Calorie-restricted diets, irrespective of the components of the diets, confound the results of these studies. Calorie-restricted diets tend to:
- lower body temperature—which lowers the energy requirements
- decrease triglycerides
- decrease serum cholesterol
- decrease insulin-like growth factor 1 (IGF-1)
- decrease inflammatory response
- decrease blood pressure
- decrease serum insulin and glucose
- reduce oxidative damage
- increase dehydroepiandrosterone (DHEA)— the most common human steroid, which decreases significantly as we age. DHEA helps combat the effects of stress.
- increase cortisol— a steroid that is associated with stress
Another point to consider is the nature of the control diet. Is the control diet a healthy diet? Does the label applied to the control diet adequately reflect the nature of the diet? The control diet may be described as low-fat or high-carbohydrate when in reality it is not. A frequently used criteria for a low-fat diet is less than 30% of calories from fat. This is not a low-fat diet.
The food we eat is a complex combination of many components— many different types of fat, carbohydrates, amino acids, and dietary fiber along with a multitude of phytonutrients including vitamins, minerals, carotenoids, and polyphenols.
A whole-food, plant-based diet will contain approximately 80% carbohydrate, 10% fat and 10% protein. The goal, however, is not to meet a prescribed macro-nutrient profile.
Another short-coming is the selective reporting of bio-markers. Only those bio-markers that appear to support the ketogenic advantage are reported—and even these are rather optimistically reported.
A study published in the journal Nutrition and Metabolism with the lead author Eric Westman is frequently cited by low-carbohydrate, high-fat diet advocates as evidence that low-carbohydrate, ketogenic diets are effective. The editorial board of this journal contains a number of low-carbohydrate, high-fat diet researchers.
Funding for this study was obtained from the Robert C. Atkins Foundation. The study compared the results of participants on a low-carbohydrate, ketogenic diet with a low-glycemic diet.
Both groups received the “same nutritional supplements known to have a mild lowering effect on blood glucose level” and a “lay-press diet book and additional handouts” were used by a registered dietician to inform the participants of the dietary requirements.
|Low-glycemic diet||Ketogenic diet|
|Wk 0||Wk 24||change||Wk 0||Wk 24||change|
|Body weight||kg||105.2 ± 19.8||98.3 ± 20.3||-6.9||108.4 ± 20.5||97.3 ± 17.6||-11.1|
Both groups were extremely overweight at the beginning and end of the trial with an average BMI of approximately 38 at the end of the 22 weeks.
There were significantly more African-American participants in the low-glycemic group. African-Americans are more susceptible to diabetes than the white American population so this factor distorts the results in favor of the ketogenic group.
Overall, the completion rate was not high. Completion rate was greater for the low-glycemic group. Only 55% of the participants were able to complete the low-carbohydrate, high-fat ketogenic diet compared with 63% on the low-glycemic diet. Given the health consequences of the participants continuing their same behavior, a greater commitment could be expected.
There was a greater decrease in triglycerides on the ketogenic diet but the starting value was significantly greater—this will again distort the results in favor of the ketogenic diet. The end results for both groups were similar.
Participants were instructed to drink “bouillon dissolved in water was recommended 2–3 times a day during the first two weeks to reduce possible side effects.” This is to supply sodium and potassium to treat the side-effects of the ketogenic diet.
Headaches, constipation, diarrhea, and insomnia were reported for both groups with a greater prevalence occurring in the ketogenic diet group. The paper stated that there was no significant difference between to two groups but the data supplied indicated otherwise.
Below is a table showing the components of the two diets.
Both groups were on a starvation diet and felt miserable. The benefits of a diet cannot be measured only in terms of the proportion of fat, protein and carbohydrates. The low GI diet is even higher in the proportion of fat and protein than the standard unhealthy western diet.
AND this was a study funded by Robert C. Atkins Foundation that supports a high-fat, ketogenic diet.
At the end of the study, both groups were overweight, diabetic and feeling miserable. Both diets have nothing to recommend in terms of health and palatability.
A true low-fat, high-carbohydrate diet has been shown to have significantly better outcomes than either of these two diets.
- high-carbohydrate diet consisting of sugar, candy, syrup, baked potatoes, bananas, and oatmeal, rice, and white bread
- high-fat diet consisting of olive oil, butter, mayonnaise, egg-yolks, and cream
- high-protein diet consisting of lean meat, lean fish, and egg-whites
- the fourth group was placed on a fasting regime
The students were fed their diets for two days and a glucose tolerance test was performed on the morning of the third day.
After only two days on their experimental diets, the only group showing a normal, healthy response to the glucose tolerance test was the high-carbohydrate group. The protein group had slightly impaired glucose tolerance whilst the high-fat and starvation diets showed a marked decrease in their tolerance for sugar.
McDougall showed significant improvement in diabetic and cardiovascular markers after seven days on a low-fat, plant-based diet. Carbohydrate intake was approximately 80% of total energy with fat representing 10% or less.
Barnard compared a low-fat, plant-based diet to an American Diabetes Association diet. The plant-based diet out performed that ADA diet and showed a significant improvement in all markers measured over the 22 weeks of the trial. Note that 16 of the 49 vegan-group participants did not strictly adhere to their diet. Their cholesterol intake was reduced from an average of 291 mg/day to 24 mg/day. The ADA group reduced their intake from an average 317 mg/day to 189 mg/day. A vegan diet contains no cholesterol.
Meckling evaluates the outcomes of a number of trials that compared low-fat diets with low-carbohydrate diets. This study included the Westman study which is discussed previously.
The tables below are derived from the papers by Meckling and Barnard.
|Dietary components||Low-fat diets||Low-carb diets||Plant-based diet|
Note the ratio for fat, carbohydrate, and protein in the plant-base diet group—18:68:14— and the large increase in the amount of fiber to 36 g.
|Metabolic factors||Low-fat||Low-carb||ADA diet||Plant-based|
It is difficult to obtain an accurate comparison between different studies because of different durations of the trials, the medications that the participants are taking often changes, and the initial state of health. Ketogenic trials focus on diabetes and obseity with the majority of participants being female and very overweight.
There are, however, several common features.
- LDL-cholesterol typically rises on ketogenic diets.
- HDL-cholesterol also increases. This is not as beneficial as supporters will have us believe.
- Serum cortisol increases which is associated with an increase in stress.
- The decrease in serum glucose is much greater on the ADA diet and plant-based diet than the “low-fat” diets and low-carbohydrate, ketogenic diets. Remember that the Westman study participants were taking nutritional supplements that decreased serum glucose.
- Completion rates are very low with “almost half of the studies included in our meta-analysis had completion rates less than 70%.”
Ketosis occurs during starvation. It is not a normal, healthy condition. No animal species or human society normally lives in a state of ketosis. Ketosis occurs when fat in the body is utilized to obtain energy in the absence of glucose. Glucose is normally obtained from the digestion of carbohydrates. Ketosis results in the production of ketones—acetone being one of the three types of ketones produced during ketosis. Blood acidity rises with an increase in ketones.
During pregnancy, ketosis has been linked to adverse outcomes for the unborn child.
Ketogenic diet trials almost invariable compare a ketogenic diet with a mislabeled “low-fat, high-carbohydrate” diet. Both the control diet and the ketogenic diet are not healthy diets—the participants are far from healthy at the start of the trial or at the conclusion.
The ketogenic trials appear to assume that the only criteria for a healthy diet is the ratio of fat, carbohydrate, and protein. Many other components are important for health such as fiber, refined sugars, phytonutrients, and protein sources.
A 2013 review of 17 studies involving 272,216 people showed that low-carbohydrate diets significantly elevated the risk of all-cause mortality.
A 2014 Harvard study examined the effects of diet on patients who survived a heart attack. Animal-based low-carbohydrate diets were associated with higher all-cause mortality and cardiovascular mortality. However, an increase in adherence to a plant-based low-carbohydrate diets was not associated with lower all-cause or cardiovascular mortality. It is important to note that the comparisons are being made to an unhealthy American diet – one that created the heart attacks in the first place.
Seventh-day Adventist’s Studies (and many others) have shown vegans have a much lower incidence of many ailments including obesity and diabetes.
Dr Katharine Milton field of expertise is the dietary ecology of primates, including human ancestors and modern humans. Professor Milton’s conclusion is:
- Westman, E. C. et al. (2008) The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus. Nutrition & Metabolism. 5 (1), 36.
- Sweeney, J. S. (1927) Dietary Factors that Influence the Dextrose Tolerance Test. Archives of Internal Medicine. 40 (6), 818–830.
- Sweeney, J. S. (1928) A comparison of the effects of general diets and of standardized diets on tolerance for dextrose. Archives of Internal Medicine. 42 (6), 872–876.
- McDougall, J. et al. (2014) Effects of 7 days on an ad libitum low-fat vegan diet: the McDougall Program cohort. Nutrition Journal. 13 (99), 1–7.
- Barnard, N. D. et al. (2006) A Low-Fat Vegan Diet Improves Glycemic Control and Cardiovascular Risk Factors in a Randomized Clinical Trial in Individuals With Type 2 Diabetes. Diabetes Care. 29 (8), 1777–1783.
- Meckling, K. A. et al. (2004) 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. 89 (6), 2717–2723.
- Hu, T. et al. (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 Epidemiology. 176 (suppl 7), S44–S54.
- Noto, H. et al. (2013) Low-Carbohydrate Diets and All-Cause Mortality: A Systematic Review and Meta-Analysis of Observational Studies Lamberto Manzoli (ed.). PLoS ONE. 8 (1), e55030.
- Li, S. et al. (2014) Low carbohydrate diet from plant or animal sources and mortality among myocardial infarction survivors. Journal of the American Heart Association. 3 (5), e001169–e001169.
- Le, L. & Sabate, J. (2014) Beyond Meatless, the Health Effects of Vegan Diets: Findings from the Adventist Cohorts. Nutrients. 6 (6), 2131–2147.
- Milton, K. (2000) Hunter-gatherer diets – a different perspective. 667.