Does diet matter? Study flags “minimal weight loss differences” between popular eating regimes

06 Apr 2020 --- There are few differences in outcomes of most diet regimes in terms of weight loss and improvements in cardiovascular risk factors over a period of six months. This is according to a study published in BMJ, which examined 121 randomized trials, involving a total of 21,942 overweight or obese patients who followed a popular named diet or an alternative control diet. The researchers highlight that people should choose a diet they prefer without being concerned about the size of benefits. 

“The extensive range of popular diets analyzed provides a plethora of choice but no clear winner. Conversations should shift away from a specific choice of diet and focus instead on how best to maintain any weight loss achieved. If we are to change the weight trajectory of whole populations, we might learn more from understanding how commercial diet companies engage and retain their customers. We can then translate that knowledge into more effective health promotion campaigns,” Helen Truby and Terry Haines comment in a linked editorial. They are both professors at Monash University and uninvolved in the original research. 

In this study, diets were grouped by low carbohydrate, low fat and moderate macronutrient, which is similar to low fat, but with slightly more fat and slightly less carbohydrate. These were then aligned with 14 popular dietary programs, including Atkins, Dietary Approaches to Stop Hypertension (DASH) and Mediterranean. 

 After 12 months, all dietary patterns and popular named diets saw diminished weight loss. In comparison to a standard eating pattern, low-carbohydrate and low-fat diets resulted in a similar modest reduction in weight – 4 to 5 kg – and reductions in blood pressure at six months. Atkins (low carbohydrates), DASH (emphasis on fruits, vegetables and low-fat dairy) and Zone (40 percent carbs, 30 percent protein and 30 percent fat) were the named diets with the largest effect on these criteria. However, moderate macronutrient diets resulted in slightly less weight loss and blood pressure reductions.

However, after 12 months, all dietary patterns and popular named diets saw diminished weight loss. With the exception of the Mediterranean diet, which saw a small but important reduction in “bad” LDL cholesterol, all the benefits for cardiovascular risk factors in the diets also disappeared. 

Therefore, the researchers state that most macronutrient diets result in modest weight loss and substantial improvements in cardiovascular risk factors, particularly blood pressure, at six but not at 12 months. This means that for short-term cardiovascular benefit, people can choose the diet they prefer from among many of the available diets without concern about the magnitude of benefits.

The road ahead
However, the researchers point to some study limitations that could affect the accuracy of the estimates. Many comparisons provided only low certainty evidence, primarily because of inconsistency and imprecision, but also because of the risk of bias. Additionally, the scarce amount of direct comparisons also negatively impacted the researchers’ ability to deal with publication bias. Notably, the authors also had no measure of a participant’s actual food or macronutrient intake.

Intermittent fasting and adhering to the Mediterranean and paleo diets can help overweight adults lose excess weight in the short term. “Analyzing individual participant data is the next step in our understanding and should produce better evidence, with a higher degree of certainty. But these analyses would require accurate information on each individual’s dietary intake,” comment Truby and Haines. 

They also note that future research should involve the role of genotype and how to predict individual responses to a particular diet or exercise regimen in order to tailor advice more accurately than is done now. This ties in with the personalized nutrition trend, which is seeing a massive spike in interest. Last month, a study called for a more personalized approach to investigate the link between nutrition and the microbiome, while UK-based Science in Sport (SiS) recently unveiled Performance Solutions, a personalized sports research and nutrition service. 

Truby and Haines note that although it is scientifically interesting to explore the distributions of macronutrients in diets, people eat foods, not nutrients. “As national dietary guidelines fail to resonate with the public, taking a food-based approach with individuals and encouraging them to consume more vegetables, legumes and whole grains and less sugar, salt and alcohol is sound advice,” they conclude. 

Obesity has tripled worldwide since 1975, which has led to a plethora of dietary recommendations for weight management and cardiovascular risk reduction. Earlier this year, NutritionInsight shone a light on some of the current top diets and which are coming next.

Another study also concluded that overweight adults following the Mediterranean, Intermittent Fasting (IF) and paleo diets were able to lose excess weight, although adhering to the diets dropped off considerably during the one-year study. 

Edited by Katherine Durrell