A new study published in The BMJ in April 2020 suggests that almost any remedial diet can result in a certain amount of weight loss and a better cardiovascular risk profile over the next six months, compared with the usual diet. However, at the 12-month mark, the dieter has mostly gained back the weight, while most cardiovascular risk factors are back at their original levels.
The only exception was the Mediterranean diet, in which the reduction in LDL cholesterol (widely associated with increased cardiovascular risk) was significant, though small, even at this point.
Mediterranean diet with vegetables and feta. Image Credit: Alicja Neumiler / Shutterstock
The researchers conclude that almost any diet will work as long as it suits the dieter and can be continued over the long term. The dieter need not, in other words, choose the ‘right’ diet in terms of which will offer the most benefit – because, in the final analysis, it seems that all of them are comparable.
The menace of obesity
The number of obese people has gone up by nearly three times over the last 45 years. With obesity being a prime risk factor for many other cardiovascular risk factors, including type 2 diabetes mellitus, cholesterol, and hypertension, many public health experts have focused on recommendations to reduce weight. The commercial weight loss market is about $72 billion.
Many of these have included advice on various types of dietary modifications. However, the number of studies directly comparing diets for their impact on weight loss and cardiovascular risk factors. As a result, the current study is aimed at examining how effective different dietary patterns are, including the commonly cited diets in vogue among overweight and obese adults right now.
The team of international researchers looked at 121 randomized trials. These included a total of almost 22,000 patients, aged 49 years on average. They were assigned to one of two groups. One group followed one or other common diet or another, while the other followed an alternative control diet.
The weight loss reported by each group of patients, and the changes in the risk factors for cardiovascular disease, were assessed.
The researchers adjusted for differences in the design of the studies and their quality. They classified the diets by the macronutrient patterns like those with low carbohydrate content, those with low-fat content, and those with moderate macronutrient content. The last had a little more fat and a little less carbohydrate.
They also categorized the diets into 14 well-known diets, such as the Mediterranean, DASH, and Atkins diet.
The researchers found that people who followed a conventional weight-loss diet, low-carb diet, and low-fat diets all succeeded in losing about 4-5 kg and in lowering their blood pressure slightly by six months. The moderate-macronutrient diet performed a little less well.
Comparing conventional diets with the named diets, they observed that the most significant weight loss came with the Atkins and Jenny Craig diets, with an average loss of 3.5 to 5.5 kg, and the most significant drop in blood pressure, at six months was with the paleolithic diet. When HDL or ‘good’ cholesterol levels, or the inflammatory marker C reactive protein, were measured, no significant change was seen at this time point or 12 months.
Overall, the Atkins, DASH, and Zone diets, as well as all diets in the low-fat category, were observed to have the best evidence and the most predictable effects on weight and blood pressure at six months. Only the Mediterranean diet had a better effect on LDL cholesterol than the usual diet.
Cholesterol formation. Illustration Credit: Naeblys / Shutterstock
When the dieters were reassessed at 12 months, all showed a reduction in the expected weight loss by 1.5 kg, and no benefit for cardiovascular risk factors, with any diet – except the Mediterranean diet.
Though the study was limited in some ways, it represents the reasonable sum of all relevant studies to date and is the result of a competent and comprehensive analysis, which lends strength to the findings.
Which diet is best to lose weight?
The study seems to suggest with a moderate level of certainty that any diet will result in some amount of weight loss and a significant reduction in risk factors for heart disease and stroke, at six months, though not 12 months. There is no significant difference between diets, which means people “can choose the diet they prefer from among many of the available diets without concern about the magnitude of benefits.”
Concerning adverse effects, a low-carb group had more side effects than the low-fat group, including constipation, headache, bad mouth odor, muscle cramps, and diarrhea.
Both the low-fat and moderate macronutrient diets produced a change in LDL cholesterol compared to the usual diet at 6 months. All the changes observed passed the limit of significance, namely, 2 kg or more of weight loss, 3 mm Hg or more reduction in systolic blood pressure, 2 mm Hg or more reduction in diastolic blood pressure, 5 mg/dL or more reduction in LDL cholesterol.
An accompanying editorial points out that the actual amount of weight loss will be different from person to person. These modest shifts in weight have beneficial health effects and should be encouraged. Moreover, human physiology shifts significantly once the individual loses weight.
In the words of the linked editorial, the analysis of a large variety of popular diets resulted in “a plethora of choice but no clear winner.” This should steer discussions about weight loss away from recommending this or that diet, and instead shift it to the best way to maintain whatever loss is achieved over the long term, whether through food choices or exercise or any combination of these.
Moreover, the widespread ignoring of national dietary guidance should prompt clinicians and dietitians to talk about food with respect to more of the desirable food categories such as vegetables, legumes, and food grains, and less added sugar, salt, and alcohol. Looking at the relative success of commercial diets, the editorial concludes wistfully, “If we are to change the weight trajectory of whole populations, we may learn more from understanding how commercial diet companies engage and retain their customers, and translate that knowledge into more effective health promotion campaigns.”
- Ge, L. et al. (2020). Comparison of Dietary Macronutrient Patterns Of 14 Popular Named Dietary Programmes for Weight and Cardiovascular Risk Factor Reduction in Adults: Systematic Review and Network Meta-Analysis of Randomised Trials. The BMJ | BMJ 2020;369:m696 | doi: 10.1136/bmj.m696
- Truby, H., Haines, T. P. (2020). Comparative weight loss with popular diets. BMJ 2020;369:m1269 doi: 10.1136/bmj.m1269