Heather Bedard, C.H.E.
The study titled, “The effect of a plant-based low-carbohydrate diet on body weight and blood lipid concentration in hyperlipidemic subjects”1, follows 47 hyperlipidemic men and women for four weeks. The study is a randomized control trial and records the benefits of a low carb, high protein plant-based diet versus a high carb, lacto-ovo vegetarian diet. I found the set-up of this particular study to be interesting because it did not include animal proteins and fats in the low carb group like many studies tend to do. There were a few points that stood out to me in reading this study.
One portion of this study records a drop in systolic and diastolic blood pressure in the low carb and high carb diet of 1.9% and 2.4% respectively. The change in blood pressure levels is not statistically significant between the two. In addition, the study is done on a small group of people (47) over a short amount of time (4 weeks). To determine if any significant changes were sustained through these different diets, I believe one would need to watch the participants over a longer period of time.
Both groups lost an average of 4kgs on the diet. The study structure lowered calorie intake to 60% of calorie requirements. While 4kg of weight loss is a worthy amount of weight loss for four weeks, most people will lose weight when on a diet that reduces their daily calorie intake by 40%.
The claim is made that the low carb, plant-based diet had lipid-lowering advantages over the high carbohydrate diet. However, it would need to be taken into account that the high carb eaters were also given a different diet which included eggs and dairy products but no meat. This would affect the LDL cholesterol levels making them higher than the low carb group. I think a study like this may need to exclude animal products completely to truly know if LDL cholesterol levels were significantly lowered in the low carb group.
This study leaves a few questions unanswered: Was the blood pressure lowered due to the dramatic weight loss or the type of diet? If the diets of both groups had not included animal products at all, how much of a difference would there have been in the drop of LDL levels?
And finally, what exactly constitutes a low carb diet? Further study shows that there is no agreed upon definition for what low carb means.2 However, many healthcare providers use similar dietary percentages.
2.
The study titled, “The effects of a low-carbohydrate ketogenic diet and a low-fat diet on mood, hunger, and other self-reported symptoms”3, records the effects of a low carb diet on mood and hunger.
The first problem I see with this study is that these results were self-reported. Self-reported information is inherently unreliable due to people’s tendency to forget or exaggerate what really happened.
Secondly, the authors don’t define what percentage of the diet included carbs; just that the diet was low carb. Without knowing if the diet was legitimately low carb, it would be difficult to accept the study results as given. There are no studies defining what low carb is as a percentage of the diet.2 The best we can do is rely on generally accepted percentages. It is also interesting to note that because the specific percentage of carbs in the diet was not given, it is difficult to say how much that percentage and also the frequency of meals, would affect hunger levels. These are details that would be helpful in determining the usefulness of this study.
Next, the study states, “An additional 51 participants who had completed an earlier trial contributed data for the psychometric analyses but were not included in the prospective analyses”. I do not believe that mixing data from different groups is best practice for a study like this. Adding the psychometric analyses of the 51 supplemental participants could skew the reporting of mood and hunger levels considering that they did not participate in the diet portion of the trial.
In regard to the authors themselves, one is Robert C. Atkins, the author of the acclaimed Atkins diet, a low carb weight-loss plan, and another is Jacquelyn A. Eberstein, the Director of Medical Education at The Atkins Center for Complementary Medicine, who worked closely with Dr. Atkins. These two individuals in particular would have a vested monetary interest in proving a scientific connection between their preferred diet plan (low carb) and mood or reduced hunger levels.
And lastly, a good portion of the information needed to determine the weight of the study is missing or too generic. While the study does state that there were 12 visits over the course of the study, it does not specify the exact length of time spent in studying the participants. Without knowing the time frame it would be hard to gauge a definitive level of efficacy. In addition to this, many of the symptoms that were presented are based on each participant’s feelings and could vary greatly in intensity from person to person. We do not know what time of day these symptoms were reported or know the exact questions that were asked. It would be difficult to determine if the opinions of the participants were logged precisely enough to lend more credence to the results.
3.
This study looks to propose that “carbohydrate restriction has a more favorable impact on the metabolic syndrome than a Low-Fat Diet.”4 The main issue with this study was found in its conflicts of interest.
The study was partially funded by the Egg Nutrition Center (eggnutritioncenter.org) which is an entire company devoted to the science of the nutrition in eggs. This could be a potential conflict due to the fact that eggs are high in protein and low in carbs making them the perfect food for low carb high protein eaters. Businesses created around eggs as their main subject for marketing would have a vested interest in funding a low-carb study, thus in turn bolstering their own sales. The study is also funded in part by the Atkins Foundation (atkinsfoundation.org). The foundation claims that it is not associated in any way to Atkins Nutritionals, Inc which is based on the proposed health benefits of a low carb diet. However, the said claim should give pause to anyone reading the study to double check its claims.
In conclusion, this study measures health markers and not necessarily outcomes. Making claims on health markers alone without looking for improvement in health overall is not giving the complete picture. This study could be improved by determining whether or not it was the lower calorie intake of the participants that had the impact on metabolic syndrome or if it was the low carb diet.
4.
A randomized control trial titled, “A low-carbohydrate diet is more effective in reducing body weight than healthy eating in both diabetic and non-diabetic subjects”5, followed 26 people for 3 months.
The study does not address the issues associated with a short-term study on weight loss. Many people lose weight in the short term when diet is changed to lower or restrict calories, but the results are not sustainable. It is unknown whether or not the weight-loss by these participants was sustained over a longer period of time. Knowing this would be more useful to those interested in weight loss on a low carb diet.
Additionally, a small cohort is studied with 15% dropping out, leaving 22 people to base results on. The abstract does not specify which four people dropped out, which could be helpful information in determining how effective the diet really was in the low carb vs. high carb groups. To that point, with such a small cohort, the difference may not be statistically significant.
Finally, the study participants given the “healthy eating diet” were given a diet based on the Diabetes UK nutritional recommendations.6 These include non-specific instructions such as restricting particular types of carbs or increasing fiber. Based on these recommendations, I am not sure how a participant would be able to determine what exactly constitutes eating less or more of a particular food group and how that data could be measured. “Healthy eating” should be defined.
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1 Jenkins DJ, Wong JM, Kendall CW, et al. The effect of a plant-based low-carbohydrate ("Eco-Atkins") diet on body weight and blood lipid concentrations in hyperlipidemic subjects [published correction appears in Arch Intern Med. 2009 Sep 14;169(16):1490]. Arch Intern Med. 2009;169(11):1046-1054. doi:10.1001/archinternmed.2009.115
2 Oh R, Gilani B, Uppaluri KR. Low Carbohydrate Diet. [Updated 2020 Jul 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537084/
3 McClernon FJ, Yancy WS Jr, Eberstein JA, Atkins RC, Westman EC. 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;15(1):182-187. doi:10.1038/oby.2007.516
4 Volek, J.S., Phinney, S.D., Forsythe, C.E. et al. Carbohydrate Restriction has a More Favorable Impact on the Metabolic Syndrome than a Low Fat Diet. Lipids 44, 297–309 (2009). https://doi.org/10.1007/s11745-008-3274-2
5 Dyson PA, Beatty S, Matthews DR. A low-carbohydrate diet is more effective in reducing body weight than healthy eating in both diabetic and non-diabetic subjects. Diabet Med. 2007;24(12):1430-1435. doi:10.1111/j.1464-5491.2007.02290.x
6 https://diabetes-resources-production.s3.eu-west-1.amazonaws.com/resources-s3/2018-03/1373_Nutrition%20guidelines_0.pdf