A group of scientists is trying to end the “diet wars” raging over how much fat and carbohydrate we should eat, arguing that what matters for most people is quality.
A review by US researchers with diverse perspectives on the fraught fat v carbs question attempts to find the common ground. Above all, they say, we should be ditching saturated for unsaturated fat and refined grains for wholegrains and non-starchy vegetables. And they list the unknowns, which need more research.
“We have diet wars,” said lead author David Ludwig, professor in the department of nutrition at Harvard Chan School of Public Health. “There are many topics in nutrition in which various colleagues take polarised positions.
“You can come up with two assessments of the world’s literature which come to opposite conclusions. This is not nuclear physics where you can objectively define your criteria for truth and all work together. Nutrition and human physiology is much more complicated than nuclear physics.”
Disagreements are not surprising, said Ludwig, but it was important to move away from entrenched positions, made worse by personal attacks on social media. Fellow author Walter Willett, professor of epidemiology and nutrition at Harvard Chan, said they wanted to review the evidence about dietary fat and health outcomes “because there has been much confusion in the media about this”.
Their review, in a special edition on nutrition of the journal Science, finds nine “current controversies” – for instance, whether fats and carbohydrates have an effect on the body that is independent of calories – and seven points on which they can agree.
“The main message to take home is that the quality of fat and carbohydrate are much more important than the percentages of fat or carbohydrate in the diet,” said Willett. “Specifically, replacing saturated fats from red meat and dairy foods with liquid plant oils, and replacing refined starches and sugar with whole grains will have important health benefits.
“There will always be questions about details, but we have strong evidence that the percent of calories from fat in the diet is much less important than the type of fat. We do have questions about the long-term effects of diets that are extremely low in carbohydrate because so few people consume these diets for long periods of time.”
Among the unknowns, they say, is whether a ketogenic diet – high fat and low carb – can provide metabolic benefits beyond those of moderate carbohydrate restriction, and especially for diabetes. And generally, they say, there has been too little research into nutrition and its effects on our health.
“There is broad agreement regarding the fundamental components of a healthful diet that can serve to inform policy, clinical management, and individual dietary choice. Nonetheless, important questions relevant to the epidemics of diet-related chronic disease remain. Greater investment in nutrition research should assume a high priority,” they write.
In the same issue of the journal, other scientists review the benefits of fasting for our health and longevity, saying that there may be potential benefits in reducing the amount we eat or changing meal frequency in the prevention of metabolic syndrome, cardiovascular disease, cancer, and even neurodegenerative diseases.
Although it is far from well understood, say Andrea Di Francesco and colleagues from the National Institutes of Health in Baltimore, “this periodic absence of energy intake appears to improve multiple risk factors and, in some cases, reverse disease progression in mice and humans.” Fasting to improve health and prevent disease looks promising, they say, but the clinical trials have not been done and people should not experiment without medical supervision.