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Currently, one in three Americans of all ages – over 100 million people – are obese.¹ As obesity rates hit peak levels, causing a major public health crisis, many Americans are looking to popular diet programs for a simple solution. There are countless diet recommendations for losing weight and reducing cardiovascular risk factors associated with being overweight such as heart disease, metabolic syndrome, high blood pressure, high cholesterol, and C reactive protein (inflammation in the body). Many popular diets have even been branded and named, promoting theirs to be the “magic key” for a healthy life and perfect body. The great majority of the promoted diets aim to either restrict or reduce the energy-providing macronutrients, e.g. fat, protein and carbohydrates without much consideration of the downstream effect of such diets on the gut’s microbial ecosystem.

With one third of Americans dieting, there is high demand for evidence-based studies reporting which popular diet programs are most effective.² In February of this year thee British Medical Journal (BMJ) released a study with 21 eligible trials with 21,942 patients comparing 14 of the most popular diet programs. Their network meta-analysis quantifies the comparative effectiveness of three dietary macronutrient patterns based on 14 popular diet programs for both weight loss and related cardiovascular risk factors at six and 12 months using the GRADE approach.

The BMJ categorized each of the 14 popular diet programs into three dietary macronutrient patterns^:3

Low Fat: approximately 60, Fat, % kcal = approximately 10-15, Fat, % kcal = <20 (Ornish, Rosemary Conley)

Low Carbohydrate: Carbs, % kcal = <40, Fat, % kcal = approximately 30, Fat, % kcal = 30-55 (Atkins, South Beach, Zone)

Moderate Macronutrients: Carbs, % kcal = approximately 55-60, Fat, % kcal = approx 15, Fat, % kcal = 21-<30 (Biggest Loser, DASH, Jenny Craig, Mediterranean, Portfolio, Slimming World, Weight Watchers, Volumetrics)

The study measured the effectiveness of each dietary macronutrient pattern to a “usual diet” by comparing its effects on: change in body weight, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, systolic blood pressure, diastolic blood pressure, and C reactive protein at the six and 12 month follow-up.

At the six month mark they found that low carbohydrate diets, compared to the normal diet, had median difference in weight loss of 4.63 kg or ~10 lbs, a reduction in blood pressure of 5.14mm Hg, a reduction in diastolic blood pressure of 3.21 mm Hg, an increase in HDL cholesterol of 2.31 mg/dL, and a reduction in LDL cholesterol of 1.01 mg/dL. Low fat diets had estimated effects similar to those of low carbohydrate diets for weight loss and blood pressure, but a greater effect on LDL cholesterol reduction (7.08mg/dL). Based on moderate to low certainty evidence, compared to low carbohydrate diets, moderate macronutrient diets had slightly smaller effects on weight loss, blood pressure, and HDL cholesterol increase but a greater effect on LDL cholesterol reduction.

Out of the popular diet programs Atkins, Zone, and DASH were most effective in reducing weight loss and blood pressure over a six month period, but by the 12 month mark weight loss and benefits for cardiovascular risk factors diminished.

In conclusion, this study found that most diets result in substantial improvements in cardiovascular risk factors, particularly blood pressure, and modest reduction in weight loss at the six month mark, but by the 12 month follow-up the effects largely disappeared for all popular diet programs except for the Mediterranean diet. Only the Mediterranean diet showed a statistically significant difference compared with the usual diet in LDL cholesterol reduction.

Although many Americans are looking for a simple solution for weight loss and decreasing their cardiovascular risk factors, most popular diet programs are not proven to be a long term, sustainable solution. Diet culture has become a dangerous belief system that prioritizes weight loss and body appearance instead of overall health and well-being. One trial even reported a statistically significant increase in the risk of several adverse effects in the group assigned to a low carbohydrate diet such as constipation, headache, halitosis, muscle cramps, diarrhea, general weakness, and rash. Unfortunately, there is no proven diet plan or restriction of a single macronutrient that is the cure all for dietary health issues.

It is of interest that only the Mediterranean diet showed a persistent beneficial effect in this analysis. The traditional Mediterranean diet contains primarily plant-based foods, including seeds, nuts, olive oil, and a moderate amount of fish and poultry. The most important health benefits from this diet are related to the high content of polyphenols and to high amounts of diverse plant derived fiber, both food components that are targeted at the gut microbiome for metabolism. (Contributing to the success of the diet is the fact that it is tasty, does not require reductions in food intake,and that it is generally consumed in social settings).

Every individual has a unique collection of microbes in their gut that reacts differently to the foods they eat and their lifestyle choices, making a “one size fits all” diet plan nearly impossible. We believe that regimented diet programs that are focused on changing or reducing the amount of macronutrients and calorie reduction are not a sustainable way to improve overall health and well-being. Instead, focusing on a largely plant based diet with low caloric density, and nutrients that feed both our microbiome and ourselves, which includes the avoidance of sugary and ultra processed foods is a much more attainable long-term approach for a healthier lifestyle.

References

1. www.tfah.org/report-details/stateofobesity2019
2. foodinsight.org/one-third-of-americans-are-dieting-including-one-in-10-who-fast-while-consumers-also-hunger-for-organic-natural-and-sustainable/
3. www.bmj.com/content/369/bmj.m696

By Juliette Frank and Emeran Mayer, MD