A study published earlier this month in the Annals of Internal Medicine reopened the question of whether or not saturated fat should be part of a healthy diet. It isn’t only the public whose head is spinning over this latest fat controversy; it’s a good portion of the scientific community.
Just last November the American Heart Association and the American College of Cardiology came out with new guidelines that recommend reducing saturated fat to no more than 5 to 6 percent of total calories.
To give you an example of just how little that it is, let’s suppose you need 2000 calories a day to maintain your weight. Five percent of that is 100 calories. An ounce of hard cheese has 100 calories and six grams of saturated fat. Those 6 grams of saturated fat contain 54 calories. That means if you eat one ounce of cheese a day you have used up more than half of your saturated fat calories. And that’s for someone who isn’t watching his weight. On a 1500 calorie weight-reduction diet only 75 calories should come from saturated fat. In practical terms this recommendation excludes regular dairy products and red meat from the diet, except as an occasional treat.
The researchers on this side of the fence, represented by Alice Lichtenstein, D.SC Director of Cardiovascular Nutrition Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts and one of the American Heart Association guideline authors, claim that there is strong evidence that saturated fat was, is and will always be a significant risk factor for coronary artery disease. Many studies—most of them epidemiological, because it is extremely expensive and unwieldy to do a clinical study in which you feed people large amounts of saturated fat over scores of years—have shown that saturated fat intake raises low density lipoprotein (LDL) cholesterol levels.
We also know that elevated LDL cholesterol levels are a risk factor for heart disease. In 1997 an article was published in the New England Journal of Medicine detailing the results of a large, well-received study involving the Nurses Health Study Cohort. Over 80,000 nurses aged 34 to 59 years were followed for 14 years. Participants were questioned about their diet using validated questionnaires and the following outcomes were found: every 5 percent increase in energy from saturated fat was associated with a 17 percent increase in the risk of coronary artery disease.
The researchers also found that replacing saturated fat in the diet with carbohydrate increased triglyceride levels and decreased high density lipoprotein (HDL) (the good cholesterol) levels. The good news was that replacing the saturated fat with unsaturated fat lowered LDL while avoiding the negative effects of increasing carbohydrate intake. Even though countless research studies have been completed since 1997, the message (at least possibly until now) has held strong: saturated and trans fats are the enemy.
The study that is causing all the current hoopla appeared in the Annals of Internal Medicine online on March 14 2014. This study is a meta-analysis of 72 previous studies, both observational and short-term interventional. When the researchers re-analyzed the results of the previous studies together, they concluded that saturated fat per say and saturated fats from dairy products in particular did not raise the type of LDL cholesterol that leads to heart disease. They also concluded that polyunsaturated fat held no benefit over saturated fats in the diet. The one point both sides agree on is that trans fat aren’t heart healthy.
What makes teasing out the relationship between fats and heart disease so complex is that there are different types of the LDL molecule and they don’t all act in the same way. Other factors that come into play are that, in addition to eating saturated fat, our bodies manufacture cholesterol- the amount based on our genetic makeup- and that the type of studies we can do (observational and short-term intervention) don’t provide proof of causality.
The crux of the argument among the researchers is a series of very complex statistical relationships, which is beyond the ken of many of us. Without a clinical smoking gun it is way too early to be stocking up on the butter, cheese and cherry pie. After all, not many studies have shown that eating mono- and polyunsaturated fat (without increasing calories) causes heart disease. The same can’t be said of saturated fat.
As Robert Gabbay, M.D., Chief Medical Officer and Senior Vice President at Joslin Diabetes Center states, “On aggregate there is still very strong evidence that saturated fats are unhealthy in a variety of ways. It’s clear all fats are not the same- monounsaturated and polyunsaturated fats are an excellent replacement for saturated fat in the diet.”
There is a good foundation of data that supports paying attention to the following healthy eating guidelines. No matter what type of fat you eat, calories continue to count. If we watch our calorie intake, our body weight will stay within a healthful range, helping to keep our lipid levels in control. If we eat the recommended amounts of fruits and vegetables we will consume a healthy amount of soluble fiber which can help reduce our cholesterol levels. If we exercise on a regular schedule we can help improve our HDL level as well as strengthen our heart muscle. So for now, enjoy that ribeye steak on your birthday, just don’t make it a habit.
Do you need help improving your diet? Make an appointment with a Joslin Nutritionist.