Now that 2021 is in full swing, people are resolving to build better, healthier versions of themselves. That resolution probably involves making dietary changes, but among all of the popular diets, which is best?

The US News and World Report recently released its ranking of the best (and worst) diets for 2021. The list was compiled by a panel of nationally recognised experts in the fields of nutrition, health, and science. This erudite group looked at 39 diets and scored them based on factors such as nutritional value, impact on short- and long-term weight loss, effect on heart health, and other key categories.

Below is an overview of the rankings and supporting scientific research, covering topics such as the best overall diet, the most effective way to lose weight quickly, and a meal plan that’s not worth anyone’s time.

The best overall diet: Mediterranean diet

To those who follow the ever-changing landscape of dietary advice, this should come as no surprise. The Mediterranean diet has been subject to numerous studies, and switching to this style of eating is said to enhance weight loss, heart and brain health, diabetes prevention and control, and other areas of health. Not only did the US News and World Report panel rank it as the top diet, the Mediterranean scored high in the rankings for best plant-based diet, best heart-healthy diet, best diabetes diet, and easiest diet to follow.

A Mediterranean diet isn’t set in stone and doesn’t involve a strict set of rules. It’s more about emphasising certain types of foods. The diet involves limiting (though not necessarily eliminating) red meats, sugars, and saturated fats. Instead, the diet focuses on fruits, vegetables, whole grains, beans, nuts, legumes, olive oil, and flavorful herbs and spices. Followers of this diet eat fish and seafood a few times weekly and include poultry, eggs, cheese, and yogurt in moderation. A couple of glasses of red wine per day are also allowed—its polyphenols are thought to act like antioxidants and help prolong life.

While the Mediterranean diet may feel like a fad, there’s mounting evidence to support claims of its health benefits. For example, a 2019 review of clinical studies, published in the journal Nutrients, examined the diet’s impact on cardiovascular disease, diabetes, and obesity. After reviewing almost 60 studies, the authors found a high level of evidence suggesting that the diet can help prevent cardiovascular disease and improve health in overweight and obese patients. Furthermore, the authors found moderate to high evidence that the Mediterranean diet can curb increases in weight and waist circumference in non-obese individuals, along with moderate evidence that it can prevent diabetes.

Similarly, the authors of a different 2019 literature review, published in Circulation Research, focused exclusively on the impact of a Med diet on cardiovascular outcomes. The authors found that adherence is associated with a range of better cardiovascular health outcomes, including significant reductions in rates of coronary heart disease, ischemic stroke, and cardiovascular disease. 

The research points in the same direction, so perhaps save that steak for a special occasion and stick to veggies and fish for regular meals.

Best diet for diabetes: Flexitarian diet

Flexitarian is a portmanteau made up of two words: flexible and vegetarian. Adherents stick to eating plants most of the time but allow themselves the occasional burger or roast. The US News and World Report panel noted that this flexibility means dieters have a lower risk of the nutrient deficiencies that can occur with vegan diets.

The flexitarian diet tied the Med diet for first place in the rankings for best diabetes diet and also shared the top spot with the Weight Watchers diet for best weight-loss diet. According to the expert panel, a flexitarian diet is an effective way to lose weight and lower risks of heart disease, diabetes, and cancer.

The diet is explained in registered dietitian Dawn Jackson Blatner’s 2009 book, The Flexitarian Diet: The Mostly Vegetarian Way to Lose Weight, Be Healthier, Prevent Disease and Add Years to Your Life. The basic tenets of the diet are self-explanatory: replacing meat with proteins like beans, peas, tofu, or eggs, and focusing on fruits and veggies, whole grains, and dairy. The book offers a 5-week plan to kickstart the diet, but followers who don’t care about losing weight quickly can ease into these habits until they become an everyday part of life. 

Much of the evidence supporting health claims around the Mediterranean diet also applies here. There have, however, been various studies that investigated the health impacts of vegetarian and vegan diets. A number of these were included in a 2019 review, published in Translational Psychiatry, that looked at the effects of plant-based diets on the body and brain. The authors found robust evidence of short- to moderate-term beneficial effects of plant-based diets on weight status, energy metabolism, and inflammation in healthy individuals, obese individuals, and patients with diabetes.

One 2019 study, published in the Journal of the American Heart Association, looked specifically at the links among a vegetarian diet, cardiovascular disease, and all-cause mortality. The authors found that plant-based diets were associated with a 16% lower risk of cardiovascular disease, a 31% lower risk of cardiovascular disease mortality, and an 18%-25% lower risk of all‐cause mortality.

Best diet for heart health: DASH diet

An acronym for “dietary approach to stop hypertension,” DASH aims to tackle high blood pressure by building eating habits around vegetables, fruits, whole grains, lean protein, and low-fat dairy. These foods feature high levels of nutrients like potassium, calcium, protein, and fiber, which help lower blood pressure. The DASH diet also limits the intake of foods high in saturated fats, sugar, and salt—the latter of which is capped at 1,500 to 2,300 mg a day.

The diet, which is promoted by the National Heart, Lung and Blood Institute, doesn’t require an immediate lifestyle shift. Practitioners can slowly introduce elements of DASH. But the targets are six to eight servings of whole grains and four to five servings of fruits and vegetables daily. DASH dieters must also strive to limit daily portions of lean protein to 6 ounces or fewer and limit their alcohol intake.

Some clinical studies support claims that the DASH diet benefits heart health. For example, a 2019 study published in the American Journal of Preventive Medicine followed about 4,500 individuals over 13 years. Researchers found that those who adhered to the DASH diet had a far lower risk of heart failure compared to those who did not. Likewise, a 2020 Nutrition Journal review of the DASH diet and hypertension concluded that even “modest adherence” to the diet is associated with a lower risk of all-cause and cause-specific mortality.

If heart health is the goal, the DASH diet might be the answer.

Bottom of the pile: Dukan diet

If the previous three diets topped the list of 39 compiled by US News and World Report, which diet came in last? The answer is the Dukan diet, which claims that the key to effective weight loss isn’t calorie counting, but focusing almost entirely on protein and eliminating carbs.

Created by former physician Pierre Dukan, who was removed from the French medical register in 2014 for promoting the plan commercially, the diet involves four phases. The first, named “Attack,” calls for all-you-can-eat protein, with vegetables allowed only on certain days. The second, “Cruise,” allows the dieter to add non-starchy vegetables but keeps other food types off the table. The third, “Consolidation,” allows limited amounts of fruit, bread, cheese, and grains, along with unlimited meats and vegetables. The final phase, “Permanent Stabilization,” has only two rules: Adherents must consume three daily portions of oat bran and eat nothing but meat protein for one day per week.

Dukan claims that practitioners can lose up to 10 pounds during their first week on the diet, and then an additional 2 to 4 pounds each subsequent week. The magazine’s panel of experts, however, ranked this diet last in nearly all categories, including diets for heart health, diabetes, and overall health.

Why? The diet has been through no extensive study, which makes it hard to judge its efficacy. Panelists also had very low confidence in the diet’s ability to manage or prevent cardiovascular disease or diabetes, or even help individuals lose weight. Among the panelists’ biggest concerns is the fact that the Dukan diet eliminates entire categories of food, resulting in an incomplete nutritional profile. One panelist noted, “It is the opposite of recommendations for a healthy diet.” Another simply called the diet “idiotic.”

This story is contributed by Alistair Gardiner and is a part of our Global Content Initiative, where we feature selected stories from our Global network which we believe would be most useful and informative to our doctor members.