Of more than 40 diets evaluated by U.S. News & World Report, popular low-carb Dukan and 'keto' diets tied for last place - while top-ranking options emphasize fruit, grains and vegetables.
The diets were ranked from best to worst based on the ease of weight loss and compliance, as well as the long term health effects - and considered such factors as dieter support systems, nutritional value, and impact on heart disease, and diabetes.
The 'keto' diet is so named as it is designed to put the body into a state of ketosis - promoting fat burn through heavy consumption of animal products and restriction of carbohydrates.
It was criticized by CNN contributor and nutritionist Lisa Drayer for being unsustainable and restrictive.
She said: "It doesn't teach you how to acquire healthy eating habits. It's good for a quick fix, but most people I know can hardly give up pasta and bread, let alone beans and fruit."
The Dukan diet focuses more on protein and includes a 10-day window of unlimited consumption of certain animal products - predominantly meat.
In this case, expert critics were concerned about malnutrition, bad breath and constipation, with some also claiming 'there’s no evidence it works'.
Higher-ranking diets were not as reliant on animal products, prioritizing instead fruits, vegetables, and grains.
The Ornish diet, which is predominantly plant-based, was praised for being heart healthy and highly nutritious, and took spot number nine on the list.
The top three diets, the Mediterranean, DASH, and Flexitarian diets, all put a strong emphasis on plants and include 'lean' animal products only in moderation.
A fully vegan diet, however, did not make it into the top 10.
In a tie for spot number 19, vegan eating was criticized for not providing 'built in support' - despite the existence of initiatives like Challenge 22 and Veganuary, in which volunteers give their time and energy to those embarking on a plant-based lifestyle.