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How We Evaluate Popular Diets

Table of Contents

What information we considered

As we set out to write this Special Health Report, our first step was to decide which diets to include. Rather than attempt to rate every single diet out there, we focused on a mix of old and new plans that have gained popularity in recent years. To evaluate these diets, we took several factors into account.

Strength of Evidence

We looked at the research supporting each diet plan, including the type and amount of evidence available. Is the research direct, testing the diet itself to see if it produces a particular health benefit or weight loss? Or is it indirect evidence, showing that similar diets are helpful? It's important to recognize that different types of studies carry varying degrees of reliability. We also considered whether research findings were taken out of context or applied to a narrow group of people.

General Nutrition Science

We used general nutrition science to assess the healthfulness of a diet plan, even if there were no specific studies on it. For example, research shows that eating plenty of plant-based foods is beneficial, so any diet that incorporates these foods is likely a good choice, as long as it's balanced.

Balanced Diet

We evaluated whether each diet plan was balanced and provided adequate nutrients. Some diets exclude entire food groups, making it more challenging to obtain essential nutrients, and therefore, requiring more planning. A diet may be balanced if executed correctly but unbalanced if it's not followed as intended.

Affordability and Ease of Implementation

We also considered the cost and availability of foods, as well as other factors that could make a diet plan more or less challenging to follow. For instance, some diets may require expensive, organic foods, or the core foods of the diet may not be readily available. Additionally, we looked at the time and skills required for food preparation, which can impact how realistic it is to stick to a particular diet.

Long-term Sustainability

Finally, we considered whether each diet plan was sustainable over the long term. Some diets may result in short-term weight loss, but are not realistic or sustainable for long-term use. We looked for diet plans that could be maintained over time, providing lasting health benefits.


Choosing a diet plan can be a daunting task, but with the right information, you can make an informed decision that supports your overall health and wellness. By evaluating factors such as the strength of evidence, general nutrition science, balanced nutrient intake, affordability, ease of implementation, and long-term sustainability, you can find a diet plan that works best for you. Remember, the most important thing is to find a plan that is realistic and enjoyable to follow, so you can achieve your health goals and maintain them over time.

William H. McDaniel, MD

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School.

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