A study released this month in The Lancet found a link between high carbohydrate intake and risk of death. The resulting headlines had dedicated low-carb dieters celebrating and low-fat vegans spoiling for a fight. But as with most dietary studies, there is more to it than the headlines claim.
The Story: The low-carbohydrate vs. low-fat headline showdown has been going on nonstop for the past few decades (at least). Constant news stories purportedly show that butter is bad, or butter is back, or butter is a part of the Matrix, and people are bamboozled every time. In reality, four of last year's flip-floppiest studies on butter turned out to mostly agree with each other when you look beyond the hype.
New nutrition studies often build upon or agree with what scientists already know, rather than completely upending the field. Today's story is no different.
We've noted before that there are only three things everybody agrees about when it comes to nutrition. Thanks to a meeting of nutrition researchers, we can add a few more things to that list.
In the study, researchers collected detailed diet questionnaires from over 135,000 individuals across 18 countries. Researchers then followed participants over several years and collected data on events such as heart attack, stroke, death from cardiovascular disease, and death from all causes. Even though everyone's lifetime risk of dying is 100 per cent, researchers can calculate whether diet seems to make people more or less likely to die during any given time.
Here's what they found. On average, people eating more than 77 per cent of their daily kilojoules from carbohydrate had a 30 per cent greater risk of dying over any given time than people who ate less than 50 per cent from carbs. Unsurprisingly, researchers also found the opposite was true: On average, people eating greater than 35 per cent of their daily kilojoules from fat had a lower risk of dying compared to people consuming the lowest amount, about 11 per cent of daily kilojoules from fat.
Now that fat is overcoming its bad reputation, it's becoming trendy to add it to food and drinks for health reasons — whether that's putting butter in your coffee for dubious benefits, or swapping 'Lite' salad dressing for a drizzle of bacon grease. But when does adding fat make sense, and when is it a bad idea?
First, since a low-fat diet is typically considered to be a diet with less than 30 per cent of kilojoules from fat, participants could still report eating a traditionally low-fat, high-carb diet and experience no increased risks at all. The "protective" effect of increased fat intake applied to everyone who ate more than 23 per cent of their kilojoules from fat. And people who ate as much as 62 per cent of kilojoules from carbs, and as low as 16 per cent from fat, saw no detrimental effect. For some context, the National Center for Health Statistics at the CDC report that the average American gets about 50 per cent of his or her daily kilojoules from carbohydrate and 34 per cent from total fat.
It's also unclear if the increased risks seen in this study can truly be applied to worried folks in the Western world reading these headlines. Among the 18 countries studied, several were very low-income or middle-income countries where diets high in refined carbohydrates (such as white rice) were eaten due to low access to more varied, nutritious diets. So some of these high-carb diets may go hand-in-hand with malnutrition. Participants in developing nations may have had differential access to things such as basic health care, clean water and air, or getting enough food to meet their energy or micronutrient needs, and these factors could have contributed to their greater risk of dying.
If you'd like to dig even further into the study design, findings and possible confounding variables, I wrote about them in more detail here.
The Takeaway: An extremely low-fat, high-carbohydrate diet with less than 20 per cent of kilojoules from fat was associated with an increased risk of non-cardiovascular death, but moderate fat and carbohydrate intakes were not associated with increased risks. It would be better to ignore the attention-grabbing shock headlines in favour of more measured coverage, such as this headline from Science Daily: "Moderate consumption of fats, carbohydrates best for health, international study shows."