By now you’ve already heard that low-carb diets are out—as are high-carb diets, if trends like Paleo, Whole30, and keto have anything to say about it. And one study, dubbed the PURE Study, is aiming to quiet the constant flip-flop of this sort of diet advice.
The study looked into how the diets of people around the world—specifically how much fat and carbs they ate—impacted their health. The researchers, from McMaster University’s Population Health Research Institute, followed more than 135,000 men and women throughout 18 countries over the course of about seven years. The participants, from those in North America to those in South Asia, completed food questionnaires and reported major health events like heart attacks or strokes.
Though it’s not the first study of its kind, the PURE Study was the first to represent such wide-ranging geographic and class-based diversity.
Here’s the thing: Studies like this can’t determine cause and effect—but they can identify patterns and connections. The PURE Study didn’t find any connections between carb and fat consumption and cardiovascular risk, but it did identify two striking connections: one between high-carb diets and higher risk of total mortality (a.k.a. dying of any cause), and one between higher-fat diets and lower risk of total mortality.
Carbs—especially the refined ones—have come under fire in the nutrition world lately, and the PURE Study backs up the idea that eating tons of carbs can backfire on our health.
The study found that when people consumed more than 60 percent of their total calories from carbs, their risk of mortality increased, explains lead study author Mahshid Dehghan, MSc., Ph.D. (For someone that eats a 2,000 calorie diet, that’s about 1,200 calories or 300 grams of carbs a day.)
Who eats the most carbs? People in China, South Asia, and Africa—where poverty and food scarcity are more widespread—were more likely to be eating upwards of 60 percent of their calories from carbs. Most people in the U.S. don’t eat quite this many carbs, though. The study found that the average person in North America or Europe got about 52 percent of their total calories from carbs (which is about 1,040 calories or 260 grams).
Why? Though the study didn’t address the types of carbs people ate, it’s likely that people in these lower-income countries relied on refined carbs like white rice and bread, which tend to be more available and affordable, according to Dehghan.
For optimal health outcomes, the study suggests that a diet consisting of 50 to 55 percent of daily calories from carbs is the sweet spot, says Dehghan.
Contrary to decades of diet advice telling us to go low-fat, the PURE Study actually found that people who ate a higher-fat diet had a lower risk of mortality.
In fact, people who ate about 35 percent of their daily calories from fat (that’s about 700 calories or 78 grams) had a 23 percent lower risk of mortality than people who ate 11 percent of their daily calories from fat (about 220 calories or 24 grams). Just keep in mind that as people ate more fat, they ate fewer carbs, says Dehghan.
The researchers also dove into saturated fats, finding a connection between low saturated fat consumption and increased risk of mortality. “While there seems to be a benefit to consuming about 10 percent of calories from saturated fat, mortality risk almost doubles when you drop down to three percent,” says Dehghan.
Those in lower-income nations, the study found, tend to eat less saturated fat. (In fact, the average person in China only got about six percent of their calories from saturated fat).
On the flipside, people in North America and Europe, where foods containing saturated fats tend to be more accessible than in other parts of the world, get about 11 percent of their daily calories from saturated fat.
The debate about how much saturated fat is too much continues to ping-pong, with some recent research questioning whether saturated fat is as bad for heart health as previously thought, and many health organizations (like the American Heart Association) disagreeing. Not only does this study fail to identify a connection between saturated fat intake with cardiovascular disease-related death, but it also calls attention to the potential dangers of eating too little saturated fat, which might be a first.
The study supports the more-popular-than-ever argument for a diet higher in fat and more moderate in carbs. What’s more, it emphasizes the impact global poverty and food access has on diet and health.
From here the researchers will be looking into associations between specific types of food (like whole grains, sugar, and refined grains) and health, according to Dehghan.
(Read more specifics on the study from The Lancet.)
Interview: Dr. Mahshid Dehghan, MSc., Ph.D. – lead study author
Walk me through the basics of the study.
Prospective cohort study – included 135000 men and women from 18 low to high income countries in both urban and rural areas – collected health history and lifestyle factors – measured diet by country through questionnaire – we used a validated questionnaire for each country because cuisine is so different
5700 deaths and 4800 major CVD
Strength of study is size and international factor
Higher consumption of fat compared with low intake is associated with lower mortality risk – about 35% from fat had 23% risk of mortality (around 11%)
Increased carbs associated with increased risk – including people from low and mid income countries, we have people with very high carb consumption, it’s not common for people in the US to eat 68% calories from carbs – we had a wide range of nutrient intake by including all of these factors
What were the findings related to carb intake?
Was there a particular threshold at/above which carb intake was associated with mortality?
More than about 60% of total calories = adverse impact on total and non-cardiovascular mortality – the highest risk from 68% + — quintiles 4 and 5 have highest risk of mortality
- More than half of the study participants at this much carbs or more
- Mean carb intake varied from 46 to 77% of total calories
- 50-55% carbs more appropriate
Did the source/quality of the carbs come into play?
Sources are important because we need to differentiate whole grains from refined carbs – we did not report different sources here, but are publishing soon
Low and mid income countries, majority of carbs come from refined carbohydrate – like rice and bread
What were the findings related to fat intake?
At/above what threshold was fat intake associated with lower mortality risk?
- 35% fat (along with a concomitant decrease of carbs) inversely associated with total mortality
What did you find regarding saturated vs. unsaturated fat?
We observed that an association with all fats and lower mortality – true for all 3 types
Association stronger for unsaturated – but still for saturated
We showed that low fat consumption is harmful – what we know is mainly data from North American and Europe where people consume more saturated and total fat than low income countries – our finding wasn’t shown before – those with very low saturated fat consumption had higher risk of mortality – we are not suggesting high saturated fat consumption – 11-13% of energy, but if lowered to 3% there is a negative association
Were any of the findings particularly surprising to you?
Yes and no
- No association between fat and major risk of CVD – clinical trials from Europe have shown that high fat consumption is protective
- Such a high carb diet was not reported on before – we are trying to emphasize that when you push people to low fat consumption, they make up for it with carbs and we are observing the impact of a high-carb diet – previous studies didn’t have this amount of data
Did any particular spread of nutrients seem to be the ideal?
The message from our study is moderation for carbs and fat – we are not supporting very low carb diet, though we see 46% of energy from carbs have lower risks, but we are not suggesting low carb diets—you need energy for physical activity which can be provided by carbohydrates
50-55% energy from carbs seems to be fine from our data – and up to 35% energy from fat
Is there a next step you see for digging deeper into what you’ve learned here?
We need to look at food – when you go to supermarkets you buy food not nutrients – we need to look at associations between foods and health events/outcomes to make it more real-life – we are looking at the different types of starches (refined grains, whole grains, sugar) and meat, and dairy and health outcomes – we have them next year