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Which Best is Best?
A new study that tracked over 5 million person years of follow-up has confirmed the best diet for your health. And this is such a relief after all of the flip-flops. So we had the fat-free craze in the '9s. Then we had the low carb Atkins explosion in the early 2000s. Now there's keto influencers and these high protein cheese puffs on the grocery shelves. There have been decades of nutrition advice and billions in revenue raked up by a food industry who are only too eager to cash in on these trends. And people are still confused. So which diet is best when it comes to your heart health? Should we aim for low-fat or should we target low carbs? And is this whole debate just been a distraction?
The Seven Countries Study
The conversation around diet and heart health began decades ago in the 1950s. A dramatic shift was happening and suddenly everyone was talking about heart disease. In England, two Oxford researchers at the time were carefully examining official records and documented a shocking increase in the numbers of deaths from heart attacks and strokes. They were killing adults in 1945 at a rate of, and get this, 15 times greater than in 1921, and the same pattern was playing out in the US. Deaths from heart disease were quite rare in 1900, and then they were the leading cause of death by the mid-century. So there was an urgent need to understand what exactly was going on.
One theory that emerged identified diet as a key culprit. Specifically, it suspected that eating more saturated fat produced higher LDL cholesterol levels in the blood, and that higher LDL cholesterol was an essential ingredient for plaque accumulation within blood vessel walls. A researcher by the name of Ancel Keys put this theory on the map through a groundbreaking research project. He set out to find groups of people living in different places who had very different dietary patterns, and in particular he was interested in how much fat they ate. He ended up assembling a massive data set of 16 cohorts of healthy men from select populations across seven countries, including several in Europe plus the US and Japan. It was called the Seven Countries Study, and the first findings dropped in 1970. In that study, heart disease was linked to blood cholesterol levels, and those in turn were linked to saturated fat in the diet. Numerous studies continued to examine the data over the years as the cohorts aged, and the relationship held. A 25-year follow-up saw the same strong link between saturated fat intake and heart disease.
Alternative Theory: Sugar as the Culprit
Ancel Keys' research pointed to saturated fat, not just any fat, as the problematic element in the diet. But the nuance was easily lost, and guidelines often recommended slashing total fat intake, fat of any kind. A statement, for example, from the American Heart Association in 1986 pushed a reduction of saturated fat and total fat, and it recommended that we replace those fat calories with complex carbs. When the flawed food pyramid was released in 1992, it proclaimed the same message. It guided consumers to minimize all fats. It also graphically represented refined carbs as the foundation for a healthy diet, which is wild. This picture dominated for decades: the best way to beat heart disease was to eat low-fat. But in the background, other researchers were quietly exploring an alternative story.
At the same time that Ancel Keys was launching his famed Seven Countries Study, a British researcher by the name of John Yudkin was poring over the statistics related to heart disease deaths. Just like Ancel Keys, he spotted an interesting link between the rates of heart disease and dietary patterns. But the thing that jumped out from the data he was looking at wasn't fat or even saturated fat. It was sugar. Yudkin's focus on carbs instead of fat as the driver of heart disease didn't gain much traction at the time. But in the late 1980s, a landmark lecture began to change the conversation. It was delivered by Gerald Reaven, who was receiving the prestigious Banting Award for diabetes research. In that lecture, he argued that insulin resistance was intimately linked to heart disease and related problems like high blood pressure. And the driver of insulin resistance, in animal studies, was a high sugar diet.
The Atkins Diet and the Low-Carb Narrative
By the year 2000, more important observational evidence was starting to come in from human clinical trials. A cohort of about 75,000 women had been followed up for 10 years, and the researchers looked at the relationship between heart disease and glycemic load. Glycemic load is a measure of how much food impacts blood sugar levels, so a high glycemic load raises blood sugar levels more sharply. At the top of the list of foods with a high glycemic index are things like white rice, white potatoes, white bread, and sugary drinks. The results were stark. The diets with the highest glycemic loads were associated with double the risk of heart disease, even after taking into account other common risk factors.
As this research was happening in the background, a cardiologist by the name of Dr. Robert Atkins popularized a new narrative inspired by it. His book, The Diet Revolution, sold millions of copies. It painted carbs as the enemy when it came to heart disease and weight loss, and it advocated for minimizing them in the diet. Fat consumption, according to Atkins, was no problem. We ended up with two competing pictures. One says low fat is the key to heart health. The other says it's low carb. This debate actually suited the food industry nicely. They've been all too happy to play along with these trends that focus on specific macronutrients. When low-fat was the focus, they lined the shelves with low-fat products, and we can see the same today with low carb. More recently, it's the high protein craze. But this whole approach is missing something profoundly important, as we'll see in a moment.
The Problem with Low-Fat and Low-Carb Labels
It seems like it should be an easy matter to figure out which of these positions is correct. But as the actual data has come in, the picture has been messy, and the results have been mixed. One massive randomized clinical trial that included nearly 50,000 participants with follow-up data of 8 years looked at the impact of reducing total fat intake. That's important: they looked at total fat intake, not just saturated fat. The impact turned out to be extremely modest. Heart disease risk did not budge, even though there were some improvements in risk factors. On the other hand, a different trial put low-fat and low-carb diets head-to-head. Those on the low-carb diet lost more weight over a six-month follow-up period, but there didn't appear to be any advantage in terms of heart disease risk metrics. All of these mixed results have prevented any clear winner from emerging, the debate has continued, and the food industry has cashed in on the confusion.
All of this probably shouldn't be a surprise, because there's a serious problem that has often muddied the waters when it comes to studies investigating the linkages between these diets and heart health. Low-fat and low-carb are just broad descriptions that can be applied to many different kinds of eating patterns. A low-fat diet, for instance, could mean a person is anchoring their meals in things like chickpeas and vegetables. A low-carb meal, on the other hand, could be salmon, avocado, and spinach, or it could be eggs fried in butter with a big side of bacon. We would expect to see profoundly different health outcomes from these different kinds of diets. It's not just the mix of macronutrients that's important; the quality of those macronutrients matters too. Past studies on diet and heart health have often not paid careful enough attention to that distinction, which is obviously critical.
The New Study: Quality Over Quantity
That brings us to the new study we're going to look at in this video, because it was specifically crafted to fill in this gap in the literature. The study authors examined data from around 200,000 people from three separate cohorts, and these cohorts were tracked for a really long time, around 30 years each. It is a ginormous data set. Critically, they used food questionnaires to distinguish diets not only in terms of macronutrient quantity but also macronutrient quality. They divided the diets into healthy and unhealthy versions of both low-fat and low-carb diets. In the analysis, healthy meant, for example, plant-based foods versus animal products, or whole grains versus refined grains. So overall, which dietary pattern won? Was it low-fat or low-carb? We'll leave out diet quality for a second here. The lowest-carb diets had a 5% elevated risk of heart disease compared to those with the highest carb intakes. Those with the lowest-fat diets had a 7% risk reduction compared to the highest-fat intakes. So low-fat seems to be the number one winner here, though the effects are relatively modest.
But all of that changes when we look at diet quality, and the picture changes radically. Those who stuck to the healthy versions of the low-carb diet had a 15% lower risk of heart disease compared to those furthest away from that eating pattern. A high-quality low-fat diet showed nearly the same benefit, cutting the risk by about 13%. The unhealthy versions of both diets raised risks to a similar degree. What's more, the healthy versions of both diets were linked to lower triglycerides, less inflammation, and other markers of better metabolic health. Before looking at how all of this applies to us, let me mention some quick caveats. First, this is an observational study, so it isn't able to tell us with much confidence about causation. It also didn't look at more extreme diets like a keto diet with exceptionally low carb intake. Finally, it doesn't mean it never makes sense to think about the macronutrient intakes of our diet. It just suggests that for most people, it's unlikely to be the most helpful thing to concentrate on.
Conclusions & Key Takeaways
So what's the big lesson here? We need to stop focusing on low-fat or low-carb. The macronutrient quantity doesn't appear to be the key factor when it comes to heart health. Instead, we have to focus on food quality. We need to prioritize plant-based proteins like chickpeas, lentils, and beans over animal sources. We want to prioritize whole foods over processed, and unsaturated fats over saturated or trans fats. Both low-carb and low-fat dietary patterns can work if we get the quality right. Returning to fat for a moment, one aspect of this study is likely to be quite controversial in the comment sections: it places animal-based food sources in the unhealthy category. This reflects a common understanding that animal products are more of a problem for heart health because of the saturated fat they contain, as well as their lack of fiber. But you'll find plenty of people online who claim this is just a myth. So what is the true story when it comes to saturated fat and heart disease?