The peer-reviewed research suggest that low-carb diets that restrict carbohydrates in favor of increased protein or fat intake were associated with higher mortality. The study looked at diets that were both high and low-carb and what replaced that that caloric intake. If the sources of protein were from animals such as lamb, beef, pork, and chicken the mortality was higher whereas diets that favored plant-derived protein and fat intake, from sources such as vegetables, nuts, peanut butter, and whole-grain breads, were associated with lower mortality.
The research analyzed the data of over 15,400 adults aged 45-64 years old. The data that was found was then compared against other studies that included over 432,000 people.