Picture an unhealthy food in your mind. If you are like most people, you probably pictured a hamburger and fries or some other fatty meal. We have been programmed to fear fat. In many cases this is true–fast food IS bad for you. Unfortunately, those great tasting fries are terrible for your body–but do we really understand why?
Some fat is bad, and some fat is actually very good for us–the key to losing weight is to understand the difference.
A Brief History of Why We Fear Fat
After World War II, in the 1950’s and 1960’s there was an increase of coronary artery disease in the United States. Physicians and researchers were desperately searching for the cause. Ancel Keys, a physician from Minnesota, hypothesized that dietary fat was to blame. He did a monumental study called the Seven Countries Study. In this study he looked at rates of heart disease and rates of dietary saturated fats and showed an association. The Seven Countries Study gained a lot of recognition in the press and was front page news for quite some time. It led to the low fat diet craze of the 80’s which has largely persisted to this day. Butter and bacon were demonized and everyone started drinking skim milk.
What was the problem? The study did not have evidence to show that saturated fat was actually causing heart disease. Dr. Keys has since been ridiculed by the scientific community, and is often held up as an example of the dangers of drawing conclusions without sufficient evidence. He also assumed all saturated fat was the same, a fatal flaw in his analysis. Interestingly, cigarette smoking had increased dramatically during WW II, and government subsidized corn farms (leading to high fructose corn syrup, etc) had also increased during this time and both are now known to increase coronary artery disease.
For an in-depth article on this history, read this NY Times article.
Not All Fat Is Created Equal
There are three main types of fat: Unsaturated fat, Trans fat, and Saturated fat. These are named by the amount of hydrogen attached to fat molecule. This may seem quite scientific, but its worth knowing about as this is how fats are listed on nutrition labels. Having a basic knowledge will help you choose healthy foods.
Unsaturated fats contain the category of fats often known as the “heart healthy” fats. There are two types of unsaturated fats: monounsaturated and polyunsaturated. The problem with the unsaturated fats is that they do not have a long shelf life, and tend to spoil quickly. Therefore, they are not used much by food manufacturers.
Monounsaturated fats: These are the healthy fats. They are found in food you have often been told are good for you–nuts, seeds, fish, olive oil, and avocados.
Polyunsaturated fats: These are not considered healthy fats. They are found in vegetable oil, canola oil, and salad dressings. They are more processed, and contain omega-6 fatty acids which have been shown to promote inflammation and can be harmful to your health. These should be eaten sparingly.
To improve the shelf life of the polyunsaturated fats, food manufacturers create highly processed man made trans fats. These will last a long time without going rancid, so they are preferred by food manufacturers. Similar to the polyunsaturated fats, they promote inflammation and are harmful to your health. These include vegetable shortening and margarine. These fats are also found in fast food (did anyone else watch in complete disbelief the end of the documentary Super Size Me where the French fries did not go bad for weeks? It forever ruined fries for me) and many packaged foods. This is exactly the reason fast food and most foods that come in a wrapper are not good for you.
Saturated fats are the class of fats that were victimized by the low fat craze of the 80’s. In medical school (at least when I went through!) we were taught that these caused heart disease and should be avoided. It turns out not all saturated fats are the same. If you look at the length of these fatty acid chains, you find a difference between odd and even length saturated fats.
Odd length saturated fats: These have been found to be healthy. They are found in the foods we previously were led to believe were harmful including cheese, animal meats, butter, coconut oil, whole milk, and eggs. Saturated fats have been shown to be associated with a lower risk of developing type II diabetes. This is a very exciting and newly evolving area of study. As the evidence continues to mount, we will see more dietary guidelines reflecting this change.
Even length saturated fats: These can be found in some foods, but more commonly they are produced by the liver after eating high carbohydrate meals for storage. These have been associated with higher risk of type II diabetes, and are unhealthy. The foods that seem to stimulate the production of these even length saturated fats are soft drinks, margarine, and potatoes among others.
How Does Fat Affect Our Insulin Levels?
If we understand that having too much insulin, and the resulting insulin resistance, is what drives obesity, we can start to tailor our diet to maintain a healthy weight by moderating our insulin response to foods. Dietary fat does not raise insulin levels because it is metabolized differently than carbohydrates. Dietary fat is broken down by pancreatic enzymes and enters the bloodstream. They do not go through the liver and do not stimulate insulin. If insulin has not been stimulated, and you ate only a reasonable amount, you will burn the fat for fuel.
Fat also increases your satiety or the feeling of fullness. If you eat a low carbohydrate, high healthy fat meal you will feel full for several hours. Many patients ask me how they can possibly go without snacking as they typically get hungry just a couple hours after eating a meal. This is the key–a high carb meal (think cereal in the morning, waffles, or a muffin) leaves you hungry in typically 1-2 hours. You start searching for a mid-morning snack and you are HANGRY by lunch. Contrast this with eating whole eggs with a handful of nuts, a coffee with cream, or even a small amount of bacon and I guarantee you will stay full until lunchtime. Your insulin levels will remain low, and you will have improved mood and improved concentration.
Adding Fat to your Diet
The key with adding fat to your diet is to make sure you are adding healthy fats and in moderation. If you eat too much of anything, your body will be forced to store it. This is not giving you the freedom to eat 20 slices of bacon every morning! However, a slice or two is OK to have. Here are some other healthy foods to incorporate more liberally into your diet:
- Olive Oil
- Most Nuts
- Seeds–pumpkin, sunflower, chia, etc
- Whole Milk
- Coconut Oil, full fat coconut milk
- Unprocessed cheese
- Fatty Fish–Salmon, sardines, etc
- Sugar Free nut butter
- Grass fed beef
- Avocado Oil
Fats To avoid:
- Fast Food
- Packaged Foods
- Processed vegetable oils with trans fat
- Vegetable shortening
- Shelf-stable salad dressings (Tip: Buy full-fat salad dressing that is refrigerated–usually found near the produce)
Give some of these foods a try for your meals and see how your body responds to them. It may surprise you!