It will likely be some time before common wisdom admits that a proper diet, as it relates to health, is multifactorial. Scores of diet books released every month, which sell thousands of copies until the next crop of diet books is published, usually point to a single factor: sugar, processed food, blood type, ketosis, kale. 

Nutrition is complex. Genes matter, but so does environment. What you ate growing up. How much sleep you’re getting. Cortisol levels. The amount of sex you’re having. Psychological stability. Microbiome. Fitness regimen. Technology addiction. Health is not just what you put into your body. This is why diet books, and diets in general, mostly do not work. 

This is not to imply that your diet doesn’t matter. It’s an important factor, arguably more relevant for body composition, obesity, and mental health than others. While the benefits and detriments of what we eat is often debatable, there are certain facts we can be confident about, such as the damaging and deadly effects of too much sugar. 

One major problem is study size. A sample of a hundred people is not going to be that trustworthy. But the recent Prospective Urban Rural Epidemiology (PURE) study followed 135,335 adults in eighteen countries. It factored in what few other studies do: income level. And it followed each individual for over seven years, linking diet with mortality and cardiovascular disease, as well as strokes and non-cardiovascular disease mortality. 

Specifically the team, led by Dr Mashid Dehghan, an Investigator for the Nutrition Epidemiology program at the Population Health Research Institute, looked at the effects of nutrients: 

Participants were categorised into quintiles of nutrient intake (carbohydrate, fats, and protein) based on percentage of energy provided by nutrients. We assessed the associations between consumption of carbohydrate, total fat, and each type of fat with cardiovascular disease and total mortality. 

Their conclusion upends decades of dietary guidelines: 

High carbohydrate intake was associated with higher risk of total mortality, whereas total fat and individual types of fat were related to lower total mortality. Total fat and types of fat were not associated with cardiovascular disease, myocardial infarction, or cardiovascular disease mortality, whereas saturated fat had an inverse association with stroke. Global dietary guidelines should be reconsidered in light of these findings.

PURE participants who consumed at least 35 percent of calories from fat were 23 percent less likely to die than those who received 10 percent or less from fat. Interestingly, the higher the fat intake, the less their chances of a stroke. More revealingly, those who took in 77 percent of calories from carbohydrates were 28 percent more likely to die than those who consumed under 46 percent. 

Being an observational study, researchers stopped shy of speculating on cause and effect. They point to previous advice regarding lower saturated fatty acids being key to health is based on only one ecological study and a handful of observational studies in only a few countries. They also challenge the notion of a linear relationship between cardiovascular disease and LDL cholesterol. 

Interestingly, researchers even challenge the wisdom of eating too many vegetables. There was no difference in mortality rates between those who ate three-four servings of veggies and those eating eight or more every day. Instead they placed emphasis on the role of fruit and seeds. 

In a nutshell, a healthy diet based on the PURE results would be rich in fruits, beans, seeds, vegetables, and fats, include dollops of whole grains, and be low in refined carbohydrates and sugars.

As stated, health is multifactorial. Income levels matter. Employment conditions matter. Stress matters. But the more researchers tease apart these factors and hone in on an optimal diet, it’s clear that a carbohydrate-heavy diet, especially one including processed foods and added sugars, is not leading anyone on the road to optimal health. 

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Derek is the author of Whole Motion: Training Your Brain and Body For Optimal Health. Based in Los Angeles he is working on a new book about spiritual consumerism. Stay in touch on Facebook and Twitter.