What is the Diet-Heart Hypothesis?

Cardiovascular disease (CVD) continues to have a massive impact in the US. Just take a look at a few of these statistics from Chris Kresser:

• Cardiovascular disease affects 65 million Americans.
• Close to one million Americans have a heart attack each year.
• In the U.S., one person dies every 39 seconds of cardiovascular disease.
• 1 of 3 deaths that occur in the U.S. is caused by cardiovascular disease.
• 1 in 3 Americans has metabolic syndrome, a cluster of major cardiovascular risk factors related to overweight/obesity and insulin resistance.
• The total cost of cardiovascular disease in 2008 was estimated at $300 billion.

On top of that, a 2004 study that looked at the connection between heart disease and lifestyle suggested that up to 90% of CVD cases are caused by (modifiable) diet and lifestyle factors. Given this, you might be wondering, how can you improve your own CVD risk and optimize your health? Don’t worry, we’ll get there!

But today, we also want to cover how we got here, the outdated model we’ve been working off of (spoiler alert: it’s the diet-heart hypothesis, and we’re operating on outdated science that’s dozens of years old!), and what you should focus on instead for CVD prevention.

What is the diet-heart hypothesis?

Simply put, the diet-heart hypothesis is the assumption that dietary cholesterol and saturated fat cause heart disease. Taking it further, it asserts that eating cholesterol and saturated fat raises your blood cholesterol, which then causes heart disease. While that’s a lot to unpack, let’s start with where the diet-heart hypothesis originated. 

Where did it come from?

Ancel Keys is the man most commonly credited with the diet-heart hypothesis, based on his epidemiological Seven Countries study. This study found associations between saturated fat intake and blood cholesterol, as well as between cholesterol and heart disease itself. 

It’s important to note that nutrition studies in humans generally tend to have limitations, but epidemiological studies, in particular, have even larger ones. Correlation doesn’t prove causation, and yet some epidemiological studies draw serious conclusions with data that may have other things affecting the outcome, also called confounding factors. Just to give you an example – though you may see that heart disease risk increases with higher fat intake it likely isn’t the only factor. Unless you took into account sugar intake, exercise frequency, and a variety of other factors, there’s no way of knowing that the increased heart disease risk isn’t the result of one of those other factors instead (or a combination). 

Keeping this in mind, there were a few other issues with Keys’ study. He didn’t include results from the population groups that didn’t support his hypothesis, and he also included populations that were eating differently at the time of the study than they normally would. Despite clear limitations in Keys’ study, both the US and UK introduced dietary guidelines in the ‘70s and ‘80s based on his research. Recommendations included limiting total fat intake to less than 30%, and keeping saturated fat to less than 10% of total calories. To this day over 40 years later, these fat guidelines haven’t really changed, and in fact they’ve been adopted across the world. Only recently, a previous cap on cholesterol was removed. 

Recent studies & reviews debunking the diet-heart hypothesis

While most recent research has debunked the diet-heart hypothesis, we want to focus on the two most famous examples; Minnesota Coronary Experiment and the Sydney Diet Heart Study. We’ll let their conclusions speak for themselves!

Minnesota Coronary Experiment  – “Available evidence from randomized controlled trials shows that replacement of saturated fat in the diet with linoleic acid effectively lowers serum cholesterol but does not support the hypothesis that this translates to a lower risk of death from coronary heart disease or all causes. Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.”

Sydney Diet-Heart Study – In this study, participants were asked to swap saturated fat in the diet with safflower oil and a safflower oil margarine. They found that the intervention group (those who removed saturated fat from their diet) actually had higher all-cause and CVD mortality. 

“Advice to substitute polyunsaturated fats for saturated fats is a key component of worldwide dietary guidelines for coronary heart disease risk reduction. However, clinical benefits of the most abundant polyunsaturated fatty acid, omega-6 linoleic acid, have not been established.

In this cohort, substituting dietary linoleic acid in place of saturated fats increased the rates of death from all causes, coronary heart disease, and cardiovascular disease. An updated meta-analysis of linoleic acid intervention trials showed no evidence of cardiovascular benefit. These findings could have important implications for worldwide dietary advice to substitute omega-6 linoleic acid, or polyunsaturated fats in general, for saturated fats.”

In other words? The advice to swap all saturated fats with polyunsaturated fats (or unsaturated fats in general) is largely misguided and likely doesn’t provide the promised benefit.

What should you eat?

If you don’t have to be wary of meat or healthy fats, you might be wondering what the heck you should eat. We’ve got you covered! 

Focus on quality, not quantity. Rather than counting grams of single nutrients, aim to eat a diet that’s rich in vegetables, healthy fats, and high-quality proteins. If you tolerate gluten-free grains or legumes, add those in too, focusing on portion size.

When you’re including fat on your plate, make sure you’re ditching processed vegetable oils and instead opting for things like:

• avocados
• fatty fish rich in omega-3s
• coconuts
• olives
• extra virgin olive oil
• nuts & seeds
• coconut oil
• grass-fed ghee or butter
• fat from pasture-raised meat cuts

And if you want to improve your cholesterol levels and your health as a whole, there’s plenty more you can do. As we mentioned above, work on avoiding refined grains and sugars, especially high fructose corn syrup. Exercise or move your body in a way that you enjoy. Avoid smoking and excessive alcohol consumption and work on limiting your life stressors.

Want to skip the prep and still eat balanced meals with healthy fats? We have low-carb, keto-friendly, Whole30 Approved, and paleo meals with your name written all over them! Head here to view all of our options.