In general, the study of good nutrition has been subject to a number of missteps and mistakes that make people suspicious of many recommendations coming from the nutrition community. I do believe the science has gotten better, and that doctors do have a better understanding of what a healthy diet looks like even if there is still a lot left to learn. I have developed five overarching rules of good nutrition that I learned primarily from doctors and public health researchers like Dr. Andrew Weil, Walter Willett, and Dan Buettner who make a similar series of recommendation on how to live a healthier life through good nutrition. Overall, they do not recommend a low fat or low carbohydrate diet but instead focus on finding the healthy foods for each type. Based on that fundamental insight into good nutrition, here are my five rules along with the key evidence in support of each one.
Rule #1 - Avoid processed foods. A lot of the foods we buy from the store or from fast food restaurants are filled with chemical additives that are dangerous to our health like high fructose corn syrup and hydrogenated oils. Making your food at home can make it easier to avoid those additives as well as other processed ingredients like added sugar, white rice, and refined flour. The Nutrition Science Initiative came to a similar conclusion, where they explicitly tested whether a healthy low fat diet or a healthy low carb diet would lead to greater weight loss through a randomized controlled trial, and found that both did approximately equally well and it was the recommendations to avoid processed foods like added sugar and refined flour that were most important in achieving weight loss. The Nutrition Science Initiative was founded by Gary Taubes, the author and researcher who started the low carb craze, and, to his credit, he explicitly started this research organization in order to make nutrition research much more rigorous by utilizing research methods like randomized controlled trials more extensively. This key study of theirs basically showed how it is making sure it is the healthy aspect of the diet and not whether it is low fat or low carb that determines its success, which is counter to what their founder Gary Taubes had advocated for many years before that.
Rule #2 - Eat good fats, not bad fats. Again, the emphasis here is not on a low fat diet, but finding and consuming more of the good fats like olive oil, nuts, avocados, and fish oil while avoiding fats like partially or fully hydrogenated oils, butter or dairy fat, and other saturated fats that comes from red meat. This is a key part of the Mediterranean diet, which has been shown in a rigorous randomized controlled trial in Spain to reduce the mortality rate of those who are at risk of heart disease and strokes. In this study, half the participants were asked to participate in a low fat diet and half were given extra amounts of either olive oil or nuts to add to their diet, and the study was forced to end early because the group getting olive oil and nuts did so much better.
Rule #3 - Eat good protein, not bad protein. This recommendation highlights that plant based protein (like legumes, whole grains, and nuts) is generally better than animal based protein (especially red meat), though including fish in your diet can be a healthy option as well. My favorite research on this issue comes from a long term study of Seventh Day Adventists, whose religion promotes various features of a healthy diet, and has a relatively high proportion of their members adopt an exclusively vegetarian or vegan diet. This research has shown that consuming less meat has lowered the health risks coming from high blood pressure, obesity, and diabetes, and that Seventh Day Adventists do live substantially longer than the rest of the population.
Rule #4 - Eat good carbs, not bad carbs. This rule suggests that carbs are ok to eat if done right, but you want to eat whole grains and avoid refined sugar and refined flour. Eating refined carbs and sugars causes insulin to spike, which means they are high on the glycemic index, and if people can steer themselves towards food with a low glycemic index, like whole grains, then you can get the calories you need without risking the insulin resistance that can lead to diabetes. The evidence I find particularly persuasive on this point is the graph I have in my own research linking high fructose corn syrup to obesity, where I show how higher levels of Coke consumption have a large negative impact on life expectancy. In the graph, the US has the highest levels of Coke consumption in the OECD, and also has a life expectancy 4 to 6 years lower than countries that consume the least amount of Coke.
Rule #5 - Eat more fruits and vegetables. Eating more fruits and vegetables has been one of the stalwarts of nutrition advice for a long time, and this one generally holds to be true. Fruits and vegetables contain a large number of important micronutrients that can be valuable for your health, and in a large long term study of the eating habits of nurses and how that might affect their health, eating more fruits and vegetables has been linked to less cardiovascular disease, lower weight, and less diabetes.
In some ways, these recommendations are simple and a little repetitive, but I think they provide a useful guide about how to approach building a healthy diet. The goal is not to become overly restrictive, but to find a balanced way to get the nutrients you need without causing any major health problems when you get them. I find that a Mediterranean, vegetarian, or vegan diet can all be quite healthy and help people adhere to the recommendations presented here, and leave it up to the individual what diet is best for them. Diet is important, and doctors have gotten a lot wrong in the past, but the higher quality of research done in recent years has led to a better understanding of good nutrition, and provided a stronger empirical foundation for the recommendations that are made. Following a healthy diet can help people avoid health problems that might arise in the future and live a longer life overall.
