This hypothesis, which has been around since the 1940's, was such a game changer in the medical community at the time, that a low-fat, low-cholesterol, and high carbohydrate diet became gospel for preventing and treating high cholesterol and heart disease. But there are many flaws with the diet-heart hypothesis. According to the president, Sylvan Lee Weinberg, of the American College of Cardiology, these recommendations may have lead to the unintended consequences of obesity, lipid abnormalities, type 2 diabetes, and metabolic syndrome (1).
Dietary cholesterol and saturated fat are not the enemies
I'll never forget sitting in a nutrition lecture when I was in culinary school and my teacher told us she reversed her high cholesterol by eating 9 eggs a day! How could that be since eggs are high in cholesterol and saturated fats? In fact, research has shown that egg consumption is not associated with increased risk of cardiovascular disease and cardiac mortality in the general population (2). Many studies have emerged since the diet-heart hypothesis that indicate dietary cholesterol has little impact on blood cholesterol levels. About 25% of the population, known as "hyper-responders", show a slight increase in their blood cholesterol levels in response to dietary cholesterol, but even in this group their blood cholesterol levels are not clinically significant.
What about saturated fats? The diet-heart hypothesis encourages people to replace saturated fats (found in butter, coconut oil, eggs, and meat) with vegetable oils rich in linoleic acid. Here's where food industry, consumerism, and medicine get tied in knots. As people switched over to consuming more vegetable oils, based on the recommended guidelines, the resulting consequence was a rise in inflammatory conditions, including coronary heart disease, in part due to the high level of proinflammatory omega 6's found in vegetable oils. Furthermore, recent research has shown that saturated fat intake was not associated with CHD or stroke mortality, all-cause mortality, or myocardial infarction (3). Saturated fats have become labeled as the enemy when in fact they have important metabolic functions in the body that control physiological processes like immunity to foreign pathogens. As in so much of nutritional research, distinction in types of saturated fat has been sorely lacking. The quality of your fat intake matters so when making saturated fats apart of a healthy diet, be discerning about how you source. Choose grass-fed dairy and butter, extra virgin coconut oil, and pastured meats and animal organs.
Carbs are not the enemy either
As fats and cholesterol have been let off the heart disease hook, the spotlight has been more appropriately focused on refined carbohydrates, which increase the risk of coronary heart disease. With this shift, all carbs seemed to have been grouped into a box: "do not eat". This is a perfect example of what happens when we vilify a whole food group. When science deemed fats, "bad", the medical community promoted a low fat, high carbohydrate diet. Industry capitalized on the low fat trend by putting out products with greater carbohydrates, but not the good kind. The general population started consuming much more refined carbs. The unintended consequence was atherogenic dyslipidemia (AD), which refers to elevated levels of triglycerides (TG) and small-dense low-density lipoprotein and low levels of high-density lipoprotein cholesterol (HDL-C). AD is a major risk factor for cardiovascular disease.
What I've noticed in more forward thinking medical and nutrition circles is the pendulum swinging the other way as far as recommendation for a low carbohydrate, high fat diet. Now, carbs have been villainized. One needs to step back and look at the big picture. Carbs are a large part of a nutrient dense diet, including a moderate amount of whole grains, vegetables, and fruits. In fact the traditional Mediterranean Diet, which includes a variety of whole grains, has been shown to reduce the risk of heart disease. The macronutrient breakdown is about 45% carbs, 35% fat and 20% protein. I'm going to go against the low carb, high fat argument and say, everything in moderation. I don't think the evidence is compelling enough to reduce carbohydrate intake so low, when whole, colorful forms are consumed.
Speaking of whole food sources of carbohydrates, there is good evidence that the fiber they contain can indirectly reduce the risk of heart disease via the gut. Once again, the gut microbes play a role in our systemic health! Research has found that the gut microbiota, the microbial ecosystem that lives within and on our digestive tract, influences cardiovascular risk factors through various mechanisms. Certain microbes play a role in lipid metabolism, while others act as mediators in inflammation signaling. Now there's more reason to feed and seed the gut with probiotic rich foods, which I list below. Equally as important are prebiotic foods (they feed the good bacteria). These include onions, bananas, tubers, chicory, jerusalem artichokes, and whole grains.
To help you remember what to eat for a healthy heart, here's a colorful list to keep around when shopping. Including some from each category every week is your greatest prevention of heart disease.
BEETS, SWEET POTATOES, SQUASH, TOMATOES, AND CARROTS
Red, orange, and yellow vegetables contain antioxidants, that reduce oxidative stress, and polyphenols which help increase insulin sensitivity, lower blood pressure and help lower oxidized LDL. Starchy root vegetables are good soluble fiber that promotes good gut health and lowers lipid levels. (Tomatoes can be consumed in fresh, canned, salsa, paste, or ketchup)
(Kale, Swiss chard, cabbage, broccoli, cauliflower, arugula)
Eating from the cruciferous family of vegetables is associated with lower risk of heart disease and cardiovascular disease mortality
(Salmon, mackerel, sardines, anchovies, bass, oysters, clams, mussels)
Great source of omega 3 essential fatty acids which decrease heart disease risk by decreasing inflammation and positively changing gene expression. Focus on the fish above that are highest in EPA and DHA
OLIVE OIL and other MONOUNSATURATED FATS
(Avocados, almonds, walnuts, macadamia nuts)
Monounsaturated fats reduce LDL, triglycerides, and inflammation, increase HDL (good cholesterol), and lower blood pressure.
(Sauerkraut, kimchi, kombucha, yogurt, kefir)
Helps reduce lipid levels, increase antioxidant potential and lower blood pressure
MEAT and EGGS
(Grass fed meat, Organ meats, pastured eggs, grass fed dairy)
Contains important antioxidants like CoQ10 not found in plants
1. Weinberg, S.L., The diet-heart hypothesis: a critique. J Am Coll Cardiol. 2004 Mar 3;43(5):731-3.
2. Shin, J.Y., Xun, P., Nakamura, Y., He, K. Egg consumption in relation to risk of cardiovascular disease and diabetes: a systematic review and meta-analysis. Am J Clin Nutr. 2013 Jul;98(1):146-59.
3. Nettleton, J.A., Brouwer, I.A., Geleijnse, J.M., Hornstra, G. Saturated Fat Consumption and Risk of Coronary Heart Disease and Ischemic Stroke: A Science Update. Ann Nutr Metab 2017;70:26-33