A big new study, published last month in the Lancet, suggests that cutting back on carbohydrates and eating more fat may extend your life. At first glance, this new finding might seem to validate the low-carb diet as the healthiest way to eat. But, as usual, there’s a lot more to this study than the headlines imply.
First, some background on how the study was conducted. Researchers compared dietary and health records from citizens of 18 different countries around the world over a ten-year period, collecting data on about 135,000 people.
They divided the subjects into groups based on how much carbohydrate, protein, and fat they typically ate as a percentage of their total calorie intake. Then, they looked at how many people in each category developed heart disease and/or died during the study.
What they found (and what you probably heard in the news) was that the people who had the highest carbohydrate intake also had the highest risk of mortality and heart disease and that those who ate the most fat had the lowest mortality rates.
But before you dig out your copy of the Atkins, South Beach, or Dukan Diet, here are a few details that you may not have gotten from the news coverage.
The study found that allocating more than 60% of calories to carbohydrates increases your risk of death and disease. But, as I’m sure you know, not all carbs are the same. Refined carbs like sweetened beverages, white bread, baked goods, and sweets are all known to contribute to disease risk. Minimally processed carbohydrate foods like whole grains, legumes, fruits, and vegetables, on the other hand, are all known to decrease disease risk.
This particular analysis did not differentiate between the two types of carbohydrates. A diet getting 60% of calories from soda, white bread, and candy was put in the same category as a diet getting 60% of calories from beans, brown rice, and broccoli. What's more, the study's authors point out that populations with the highest carbohydrate intakes also consume the most refined carbohydrates.
Are diets high in carbohydrates the problem or diets that are high in refined carbohydrates? I think we can all guess the answer.
This analysis also does not suggest that low carb diets are the way to go. In fact, those whose carbohydrate intakes were below 50% of calories were no healthier (on average) than those with intakes between 50-60%. According to the researchers, this analysis “does not provide support for very low carbohydrate diets.”
Are high fat diets healthier?
This study does not provide support for a high-fat diet, either. Yes, it’s true that those in the highest quintile for fat intake had a lower mortality rate than those in the lowest quintile. However, the average fat intake for this death-defying group was just 35% of calories. The average fat intake for Americans? 34% of calories. If you’re looking for support for a diet that gets 80% or more of calories from fat, you won’t find it here.
See also: Carbs or Fat: Which Is the Body's Preferred Fuel Source?
What’s a quintile, you might be wondering? To divide a group of people into quintiles, you’d line them up from lowest to highest according to any measure. You could line them up by height or by income or by percentage of fat intake. Once they are lined up, you’d simply divide them into five equal groups. So, if you had 100 people, the 20 people who earned the most would be in the top quintile for income and the 20 people who earned the least would be in the lowest quintile. To get a quartile, you divide the group into four equal groups.
The study also looked at the type of fat consumed: saturated, polyunsaturated, or monounsaturated. And the trends confirmed what we’ve been saying for a while now: Saturated fat is not as harmful as we’ve been led to believe, but it doesn’t seem to be as beneficial as unsaturated fats—in particular, the monounsaturated fats that you get from olive oil,canola, and avocado.
One of the good things about this study is that they really cast a wide net: In addition to the usual suspects (overfed North Americans and Europeans), they included people from Africa, South America, Asia, and the Middle East, so a lot of different cultural dietary patterns were represented. They selected countries with high, middle, and low per-capita incomes--and this is important because income has a big impact on both diet and health. They also adjusted the results to account for other variables like smoking, physical activity, education level, waist-to-hip ratio, and total calorie intake.
On the other hand, this is an observational study that relied on self-reported intakes. It doesn’t prove that diets that are higher or lower in carbs or fats cause or prevent death or disease. It simply shows associations between certain nutrient intakes and certain health outcomes.
Translating Data into Dinner
What, then, are we supposed to take away from this study? Contrary to what you may have seen around the Interwebs, it is absolutely not an endorsement of low-carb or high-fat diets, because virtually noone in this study was doing either one. It does make a pretty compelling argument against low-fat diets.
But the really big take home lesson here is something we already knew: Refined carbohydrates should definitely not make up the bulk of your diet.
See also: How to Reduce Your Added Sugar Intake
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