What’s the best nutrition program? Mediterranean? Low-fat? Paleo? Atkins? You’ve probably heard so much conflicting advice that your head’s spinning. So, here’s what science says about the healthiest possible diet.
Let’s start with protein. As we’ll see with every macronutrient, it isn’t how much protein you eat, but the type that matters. Take one Harvard study. It found that red meat, processed meat and high-fat dairy were significantly associated with heart disease. Poultry, fish, nuts, and beans, however, were associated with a significant decreased risk. Looking at the chart below, you can see what happens when you substitute one type of protein for another (risk is reduced as you move down on the chart). Replacing one serving a day of red meat with one serving a day of nuts, for example, leads to 30% reduced risk of heart disease. Let’s look at each type of protein.
- Red/Processed Meat: Another Harvard study found that each daily serving of red meat increased the risk of death by 13%, while each daily serving of processed meats increased the risk of death by 20%. It’s important to note that a serving of red meat in the study was just 3 oz. (about the size of a deck of playing cards) and a serving of processed meat was just 2 slices of bacon or 1 slice of cold cuts. Most people eat much more than a serving in a sitting, so your risks could be even higher than those indicated above. Red meats include: beef, pork and lamb. Processed meats include bacon, hot dogs, sausage, salami, bologna and cold cuts. If you do eat red meat, choose cuts that aren’t salted, smoked or cured, trim away excess fat, and don’t char the meat on the grill. Marinating meat can help as well.
- Dairy: Dairy product intake has been associated with a reduced risk of type 2 diabetes. A meta analysis found that dairy consumption (high or low-fat) was also associated with a 6% reduction in cardiovascular disease, but not associated with coronary heart disease, stroke or total mortality. However, another study found that high-fat dairy was associated with an 8% increased risk of heart failure. Dairy is also associated with a significant increased risk of prostate cancer.
- Eggs: Some have claimed that eggs are unhealthy due to their high cholesterol levels, while others have responded that they are high in a variety of nutrients. One meta analysis found that egg consumption was not related to cardiovascular disease among people not suffering from diabetes. However, eating 1 egg or more a day increased the risk of type 2 diabetes by 42%. Among diabetics, frequent egg consumption increased the risk of cardiovascular disease by 69%. Another study found that up to 6 eggs a week was not associated with heart failure, but 7 or more eggs a week was associated with an increased risk of heart failure. Another meta analysis found that frequent egg consumption was related to a 25% reduced risk of hemorrhagic stroke though. Overall, limit your egg consumption to 6 a week or less.
- Poultry: One study found that poultry consumption was unrelated to an increased risk of mortality. Avoid fried chicken and chicken nuggets though.
- Fish: On to the good stuff. A meta analysis found that consuming fish once a week was associated with a 15% reduced risk of coronary heart disease. Eating fish 2- 4 times a week was associated with a 23% reduced risk, while eating fish 5 times a week or more was associated with a 38% reduced risk of heart disease. Overall, each additional 20 grams of fish a day was associated with a 7% reduction in coronary heart disease mortality. Another study found that fish consumption also reduces the risk of colorectal cancer by 12%. Yet another study found that 3 servings of fish a week reduces your risk of stroke by 6%. When choosing fish, look for high levels of omega-3 fatty acids and low levels of mercury. Some great options include: salmon, rainbow trout, sardines and anchovies.
- Nuts: Studies show that people with the highest intake of nuts (5x or more a week) have a 35% lower risk of coronary heart disease. Nuts have also been shown to reduce the risk of cancer, respiratory disease and all-cause mortality. Research has shown that 1 oz. (about a handful) a day is optimal. Aim for variety.
- Legumes: One study found that legume consumption of more than 4x a week is associated with a 22% reduced risk of coronary heart disease and an 11% reduced risk of cardiovascular disease.
All types of fats were villainized for a long time. However, we now know that was wrongheaded. One study found that overall fat intake wasn’t associated with heart disease risk. Looking deeper though, trans fat and saturated fat were significant associated with heart disease. Monounsaturated and polyunsaturated fats, however, were associated with a significant reduced risk. Replacing just 2% of energy from carbohydrates with trans fats was associated with a 91% increase in heart disease risk. Replacing 5% of energy from carbohydrates with saturated fat was associated with a 17% increase in heart disease risk. Replacing 5% of energy from carbohydrates with monounsaturated fat and polyunsaturated fat was associated with a 19% and 38% reduction respectively (see chart).
- Trans fat: A Harvard study found that women who ate the most trans fat (an average of 7 grams a day) had a 50% increased risk of heart disease over a 14 year period. Trans fat has been found to raise LDL cholesterol (bad cholesterol) lower HDL cholesterol (good cholesterol), raise triglycerides, increase blood clotting, and spike inflammation. Trans fat can be found in cakes, cookies, pie crust, french fries, doughnuts, fried chicken, other fried foods, potato chips, corn chips, microwavable popcorn, non-dairy creamer, margarine and frosting. Fortunately, manufacturers have 3 years to remove trans fats from products in the U.S.
- Saturated fat: Saturated fat has long been seen as a major enemy to health. While the above study would seem to support that status, a recent meta analysis found that saturated fat was not associated with coronary heart disease, cardiovascular disease or stroke. However, a more recent review found that reducing saturated fat did in fact reduce the risk of cardiovascular events by 17%. So, saturated fat might not be as bad as once thought, but you still should avoid it to be safe. Sources of saturated fat include: red meat, whole milk, cheese and coconut oil.
- Monounsaturated fat: A healthier source of fat is monounsaturated fat. A study found that monounsaturated fats reduced cardiovascular mortality by 12%, stroke by 17% and all-cause mortality by 11%. Olive oil was found to be especially beneficial. Sources of monounsaturated fat include: olive oil, peanut oil, avocados and nuts.
- Polyunsaturated fat: Another study found that polyunsaturated fats reduced coronary heart disease by 19%, which amounts to a 10% reduced risk for every additional 5% of energy from polyunsaturated fats. Foods high in polyunsaturated fats include: walnuts, canola oil, sunflower seeds, sesame seeds, chia seeds, unsalted peanuts, salmon, mackerel, sardines, salmon, peanut butter, soybeans, seaweed, avocado oil and olive oil. Focus on increasing these fatty foods.
While low-carbohydrate diets have been shown to be effective for weight loss, a meta analysis found that low-carb diets are significantly associated with increased mortality risk. Like everything else, it matters which types you eat. On top of fruits and vegetables, there are 3 things you should look for: whole grains, high in fiber, with a low glycemic load/ index.
- Fiber: A meta analysis found that people who ate the most high fiber foods had a 23% reduced risk of cardiovascular disease, a 23% reduced risk of all-cause mortality, a 17% reduced risk of cancer, a 68% reduced risk of digestive diseases, a 58% reduced risk of infectious diseases, a 43% reduced risk of inflammatory diseases, a 47% reduced risk of respiratory diseases and a 25% reduced risk of circulatory diseases.
- Whole grains: Whole grains are grains that have not been processed (like refined grains) and so they still include the bran, germ and endosperm of the grain. One study looked at whole grain and mortality over a 25 year period. After adjusting for other variables like smoking and other dietary factors, the researchers found that greater whole grain intake was associated with a 16% reduced risk of cardiovascular disease mortality and a 9% reduction in all-cause mortality. Three servings a day have been found to reduce the risk of colorectal cancer by 17%. Whole grains have also been found to reduce the risk of type 2 diabetes. Whole grains include: wild rice, brown rice, wheat, spelt, rye, quinoa, millet and barley.
- Glycemic load: A meta analysis found that glycemic load is associated with an 8% increased risk of coronary heart disease for men and a 49% increased risk for women. Glycemic load was also associated with a 19% increased risk of stroke. The glycemic index, in contrast, was associated with a slight increase in coronary heart disease, but was unrelated to stroke. Glycemic load is also linked to breast cancer, colon cancer, pancreatic cancer and type 2 diabetes. Here‘s a list of glycemic load and glycemic index numbers for over 100 foods.
- Fruits and vegetables: You’ve been told you’re whole life to eat more fruits and vegetables. There may, in fact, be good cause for that. A meta analysis found an additional serving a day of fruits and vegetables reduces your risk of all-cause mortality by 5%. This relationship appeared to hold up to 5 servings a day. A review also found convincing evidence that fruits and vegetables reduce the risk of hypertension, coronary heart disease and stroke and probable evidence that they reduce the risk of cancer. Aim for a variety of fruits and vegetables of all colors.
There are a number of promising herbs and spices like basil, cinnamon, cloves, turmeric, oregano, rosemary, ginger, dill and coriander that look likely to improve health outcomes. However, there is not yet enough research on these herbs and spices to make definitive conclusions at this point. There are two condiments that we know can be bad for you though: sugar and salt.
- Added sugar: Believe it or not, the average American gets 10% of their daily calories from added sugars. One study found that compared to those who got 8% of calories from added sugar, those who got 17% to 21% of calories from added sugars had a 38% increased risk of cardiovascular disease mortality. The risk of cardiovascular disease for those who obtained 21% or more calories from added sugar was 103% greater. Another study followed 353,751 people for up to 13 years and tracked their total sugars, added sugars, total fructose, added fructose, total sucrose, and added sucrose consumption. The researchers found that all-cause mortality was associated with total sugar, total fructose and added fructose in women and total fructose in men. So it appears that fructose is especially harmful. Sucrose (table sugar) is 50% glucose and 50% fructose. High fructose corn syrup is 45% glucose and 55% glucose. So, both should be limited. Interestingly, these sugars were found to be harmful when obtained from beverages, but sugar was actually somewhat protective when obtained from solid food like fruit (perhaps because of the other nutrients that were consumed alongside the sugar).
- Salt: High salt intake is known to increase blood pressure. Not surprisingly then, one study found that high salt intake is associated with a 23% increased risk of stroke and a 14% increased risk of cardiovascular disease. While there is some controversy around how much salt to aim for a day (you don’t want to eliminate it entirely), the NIH and American Heart Association recommends 2,400 milligrams a day (about a teaspoon).
There are a number of eating patterns that closely match the above findings. Vegetarian and vegan diets, for example, are a significant improvement over a Western diet (pretty much everything is). One study, though, found that vegetarians and vegans had a 9% and 15% reduced risk of all-cause mortality, respectively. However pescetarians were even better off, with a 19% reduced risk of all-cause mortality. Given that, and considering that a Mediterranean diet matches every other finding listed above, it appears to be the healthiest overall eating pattern. There is also a plethora of studies showing that a Mediterranean diet can benefit just about every health factor under the sun. It has been found to reduce the risk of heart disease, stroke, cancer, type 2 diabetes, obesity, pregnancy complications, cognitive decline, Alzheimer’s disease, Parkinson’s disease and depression (among other health problems). Switching to a Mediterranean diet for just 10 days has even been shown to improve alertness, contentment, memory recall and reduce confusion.
Probably the greatest thing about a Mediterranean diet is you aren’t completely eliminating any major food group. Instead, it’s all about eating the right kinds of food. So in summary, limit/ avoid red meat, processed meat, trans fats, saturated fat, added sugar and salt. Eat more legumes, nuts, fish, monounsaturated fats, polyunsaturated fats, fruits and vegetables and high-fiber whole grains with a low glycemic load. Easy enough.
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