Review assesses low-fat/high-carb and high-fat/low-carb diets

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A strong> US research review agreed that no specific fat to carbohydrate ratio is best and that an overall high-quality diet that is low in sugar and refined grains will help most people maintain a healthy weight and low chronic disease risk.

“This is a model for how we can transcend the diet wars,” said lead author David Ludwig, professor in the department of nutrition at Harvard Chan School and a physician at Boston Children’s Hospital. “Our goal was to assemble a team with different areas of expertise and contrasting views, and to identify areas of agreement without glossing over differences.”

The authors laid out the evidence for three contrasting positions on dietary guidelines for fat and carbohydrate consumption: high consumption of fat causes obesity, diabetes, heart disease, and possibly cancer, therefore low-fat diets are optimal; processed carbohydrates have negative effects on metabolism; lower-carbohydrate or ketogenic (very low-carbohydrate) diets with high fat content are better for health; and the relative quantity of dietary fat and carbohydrate has little health significance – what’s important is the type of fat or carbohydrate source consumed.

They agreed that by focusing on diet quality – replacing saturated or trans fats with unsaturated fats and replacing refined carbohydrates with whole grains and non-starchy vegetables – most people can maintain good health within a broad range of fat-to-carbohydrate ratios.

Within their areas of disagreement, the authors identified a list of questions that they said can form the basis of a new nutrition research agenda, including: do diets with various carbohydrate-to-fat ratios affect body composition (ratio of fat to lean tissue) regardless of caloric intake; do ketogenic diets provide metabolic benefits beyond those of moderate carbohydrate restriction, and especially for diabetes; and what are the optimal amounts of specific types of fat (including saturated fat) in a very-low-carbohydrate diet?

Finding the answers to these questions, the researchers said, will ultimately lead to more effective nutrition recommendations.

 

Abstract
For decades, dietary advice was based on the premise that high intakes of fat cause obesity, diabetes, heart disease, and possibly cancer. Recently, evidence for the adverse metabolic effects of processed carbohydrate has led to a resurgence in interest in lower-carbohydrate and ketogenic diets with high fat content. However, some argue that the relative quantity of dietary fat and carbohydrate has little relevance to health and that focus should instead be placed on which particular fat or carbohydrate sources are consumed. This review, by nutrition scientists with widely varying perspectives, summarizes existing evidence to identify areas of broad consensus amid ongoing controversy regarding macronutrients and chronic disease.

Authors
David S Ludwig, Walter C Willett, Jeff S Volek, Marian L Neuhouser

Harvard TH Chan School of Public Health material
Science abstract


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