You’ve heard it argued in gyms, amongst nutrition circles, and practically anywhere people congregate online. And more often than not, you’ve heard mostly black-and-white opinions about which of the three macros is ‘the worst of the worst.’
But very rarely do we look at both fat and carbs under the same level of scrutiny. And even more rarely do we critically evaluate both in a metabolically sound, heart health context.
In this article, I’ll provide a trail of research that’s been informing both sides of the debate for the past 30+ years. I’ll present the facts so you can come to your own conclusions, then share my thoughts at the bottom of the guide.
The overview:
- There has been a wealth of research targeting both fat and carbohydrates (typically sugars) as the root cause of heart disease.
- It’s been suggested that high-fat foods may come with high saturated fat, and therefore hurt your heart. It’s also been said that high-carb diets spike your body’s insulin levels, which leads to inflammation and damages the heart.
- Whole, real food diets following low-carb and low-fat approaches show a significantly lower risk of cardiovascular disease versus lower quality food choices.
The case against fats
First, a brief background.
Fat is an essential macronutrient that provides the body with a slow-burning energy source. It provides nine calories of energy per gram, and in natural food sources often accompanies a protein source.
The biggest and perhaps most oft-cited source against fats for heart health was Ancel Keys’ Seven Countries Study. In it, Keys posits that countries consuming more saturated fat suffer more coronary heart disease.
But as we know today, the Seven Countries Study was significantly flawed, and low-fat diets can be detrimental to your health and even dangerous when severely deprived.
We also know that not all fats are the same. While saturated fat gets much of the blame for heart disease, there has been quite a bit of research surrounding other omega-6 fats such as monounsaturated and polyunsaturated varieties.
Case in point: there is evidence to suggest that limiting saturated fat has little to no health benefit for a population. One study even asserts that “continuation of a cap on saturated fat intake also fails to consider the important effects of the food matrix and the overall dietary pattern in which saturated fatty acids are consumed.” Interestingly, replacing saturated fat with mono- and polyunsaturated fat options may actually increase your risk factors for heart disease.
Learn more about how to tell the difference between good and bad fats in your diet.
The case against carbs
The carbohydrate — a macro that includes sugar, starch, and fiber — is the only nonessential nutrient in the human diet. You get four calories of energy from every gram consumed, which makes it half the density of a gram of fat.
There’s been quite a lot of talk about the ‘heart healthy’ benefits of carbs, particularly as they are the polar opposite of fat (and are thus less associated with the ‘boogeyman’ of saturated fat).
But there’s still quite a bit of research showing the dangers of a high-carb diet. In particular, high-carb diets can trigger insulin responses that, over time, drive insulin resistance, inflammation, and metabolic dysfunction. These are all known risk factors for heart disease.
You’ll notice an even more disturbing trend when reviewing the low-fat dietary guidelines of the 1970s and ’80s. As fat was removed from processed foods, most people replaced it with refined carbohydrates and sugar. Instead of improving heart health, low-fat diets are largely correlated with obesity, type 2 diabetes, and metabolic syndrome.
Considering 70% of grocery store food contains processed sugar — and most of America’s weekly food purchases are heavily carb-based — it’s no surprise that heart attack rates are steadily on the rise. Yes, this even includes those eating ‘healthy’ whole grains and ‘healthy’ sugar alternatives.
So, should you eat more carbs, or more fats?
Once again, this isn’t an easy answer. Your best bet is looking for quality and nutrient density in your food, and not necessarily the macro itself.
A study completed in 2021 put this to the test. The low-fat diet appeared to suppress appetite and greatly reduce the body fat of participants. But it also significantly spiked glucose and insulin levels, which could increase the risk of coronary artery disease. In contrast, low-carb diets kept blood glucose and insulin levels steady. But they technically came with more calories per bite, so participants ate approximately 550 to 700 more calories per day.
I would like to call your attention to the fact that these meals were carefully designed with whole, real foods.
Another study completed in February 2026 picked up on the same through-line. In it, researchers examined the diet quality, metabolomic data, and heart disease risk in nearly 200,000 US adults across more than 30 years. By the end of the study, the researchers determined that diets of whole, real foods saw:
- Higher HDL cholesterol
- Lower inflammation
- More favorable biomarker patterns
In their words, “These findings highlight the critical role of diet quality in determining health effects of low-carbohydrate and low-fat diets on CHD risk. The healthy versions of these diets may exert their health benefits through some common pathways that together entail favorable cardiovascular risk profile and lower CHD risk.”
What does ‘healthy’ mean in this context?
This largely depends on who you ask, since the definition of a ‘whole, real food’ can be easily extrapolated to fit many interpretations. But in general, I’d offer this rule of thumb: anything that comes from the ground or eats food that grows on the ground.
To apply the principles to your own life, I heavily recommend the following:
- Avoiding unnaturally processed oils. This includes vegetable and seed oil, margarine, and anything else with a high volume of ultra-processed omega-6.
- Throwing out high-carb processed food. Refined sugar, for example, shouldn’t have a regular place in a healthy diet.
- Focusing on whole, real foods. This means if you choose to eat carbs, focus on foods like berries, onions, and green beans. Whenever you eat fats, focus on animal meat, nuts and seeds, and olive or coconut oil. Also pay attention to your health status; if you have insulin resistance you should strictly limit your carbohydrate intake.
Overall, I highly recommend following a proper human diet, which you can find outlined in the new US food pyramid.
No need to take my word for it, though.
Learn more about the science of a proper human diet from Low Carb Pioneer Dr. Eric Westman.