Fats: The Good and the Bad News

  • Fat is a general name for a type of macronutrient that along with protein and carbohydrates provide energy for our body.
  • Fat is essential to health and is important for many reasons including: absorption of many vitamins, lowering inflammation, as well as by reducing electrical instability of the heart.
  • When polyunsaturated fats (PUFA) are substituted for high carbohydrate low fat diets the total number of disease-causing cholesterol particles called lipoproteins are decreased.

The public has every reason to be confused when it comes to what is “accurate” nutrition advice. The standard “knee-jerk” response from health professionals to the question of what makes up a “healthy” diet has for more than 50 years been based on the need to reduce dietary fat and cholesterol.

Food manufacturers responded to the low fat mantra with one of the most extensive public relations campaigns to promote “low fat” by creating low-fat products loaded with sugars. The reality is that this approach has failed despite decades of recommendations to reduce cholesterol and saturated fats. In the last few years, there has been a sea change in our understanding of atherosclerosis (hardening of the arteries) and obesity and type 2 diabetes and the relationship to nutrition. The connections with sugar and carbohydrates with the epidemic of heart and metabolic diseases -is taking center stage in nutrition circles. The old recommendation to just eat low fat can no longer be accepted as gospel.

A history lesson

Research on the types of fat and how nutrients are substituted within an overall diet has led to the prevailing idea that it is the overall dietary pattern (and quality) not the percentage of fat or saturated fats that really matters for health. The risk of heart disease remains the same if saturated fat is replaced with refined starch or sugar, which are the largest sources of calories in the U.S. diet. In the 1960s, Americans consumed about 45 percent of calories from fats; about 13 percent of adults were obese and less than 1 percent had type 2 diabetes. Today, Americans eat less fat, or about 33 percent of calories; nevertheless, obesity levels have nearly tripled and more than ten times more adults are diabetic. Nutrition studies that claim specific foods or diets cause or prevent disease receive much publicity but their conclusions must not be taken for granted and must be scrutinized closely. Excessive amounts of sugar, refined carbohydrates and trans fats are leading nutrition factors for the development of obesity, pre diabetes/ type 2 diabetes, heart attack and stroke.

The landmark Seven Countries Study by Ancel Keys more than 60 years ago showed an association of heart disease to saturated fat consumption. Coronary heart disease death rates correlated with percent calories from saturated fat and (not often mentioned) percent calories from sugar. Keys explained away this “inconvenient truth” by the “intercorrelation” with saturated fat. Moreover, The Seven Country Study was actually an analysis of 22 countries and the obvious criticism related to cherry-picking the data with the best fit cannot be discounted. According to the British visionary, Dr. John Yudkin, and vocal Ancel Keys critic an analysis of the same data (1957) found a much more significant association with fatal heart attacks (coronary thrombosis)  and sugar consumption (and affluence) -not with fats.  In 1961, Dr. Keys codified saturated fat’s influence and served on the first American Heart Association nutrition committee whose dietary guidelines are still considered the gold standard. Yudkin’s call to consider the totality of the evidence and importance of refined carbohydrates and sugar was drowned out (Pure White and Deadly, John Yudkin. Penguin Books, 1986).

For decades the assumption was that saturated fats raise “bad” LDL-cholesterol and the higher the LDL the greater the heart attack (atherosclerotic heart disease) risk. A critical look at the evidence casts doubt on that simple assumption. In fact, the relationship is more closely related to the numbers of LDL-particles –not the amount of cholesterol. To understand the controversy about fats and carbohydrates realize that low density lipoproteins (or LDL) consists of a distribution of LDL particles. Refined carbohydrates and sugar can increase the numbers of disease causing LDL-particles -much more than a high fat or high saturated fat diet. Hardening of the arteries or atherosclerosis is more closely related to the LDL-particle number (LDL-P) rather than the mass of cholesterol (LDL-C).

Moreover, saturated fats are not one entity: recent evidence shows that saturated fats from dairy consumption, for example (saturated fats from dairy have an odd number of carbon atoms) are associated with less type 2 diabetes and cardiovascular diseases. Some saturated fats in fact, do not raise cholesterol at all. Stearic acid (found in chocolate) for instance, does not raise LDL-cholesterol and randomized controlled studies show dark chocolate lowers many risk factors of cardiovascular disease. We cannot expect health benefits from blindly restricting the amount of saturated fat in the diet -as past dietary guidelines suggested. It turns out that what is substituted for saturated fats is far more important. Saying it another way, it is the interplay of an overall healthy dietary pattern that is the underlying nutrition principle.

The total nutrition pattern

An analysis involving almost 350,000 people who were tracked from five to 23 years found that those who consumed the most saturated fat actually did not have a higher risk of heart disease, stroke or any other form of heart or blood vessel disease. (American Journal of Clinical Nutrition, 2011). There is increasing evidence to support the idea that the total matrix of a food is more important than just its fat content when predicting the effect of a food on coronary heart disease risk. According to Dr. Ron Krauss, Senior Scientist and Director of Atherosclerosis Research at Children’s Hospital Oakland Research Institute, and Adjunct Professor in the Department of Medicine at UCSF, “rather than focusing on saturated fat as a top priority for heart disease risk, one really needs to look at overall diet in which saturated fat is eaten.”

To understand the controversy about fats and carbohydrates realize that low density lipoproteins (or LDL) consists of a distribution of particles). Dr. Krauss has demonstrated that an increased consumption of sugar and refined carbohydrates compared to a high fat diet can actually change the composition of LDL and change the distribution of LDLs into smaller, denser and more numerous LDL-particles to a greater extent.  Substitution of polyunsaturated fats (PUFA) for saturated fatty acids (SFA) for example has been shown to lower cardiovascular risk but when carbohydrates are substituted no benefit can be shown. This is believed by many to be directly related to the change in composition of LDL into more disease-causing LDL-particles.

Limiting saturated fats in the diet may lower LDL cholesterol and the so-called good cholesterol (called HDL-C) but the evidence on any positive health benefit is limited and muddied (or confounded) when carbohydrates are substituted for saturated fat calories. “Eat low fat” is no longer an agreed upon nutrition message: it’s less about macronutrients and percent calories from fat and more about one’s total dietary pattern. The science put forward by Krauss and others support the importance of a healthy dietary pattern rather than a focus on percent of saturated fat and brings home the important message about how nutritional quality intersects with LDL particles .

If saturated fat is replaced with polyunsaturated fat or monounsaturated fat in the form of olive oil, mixed nuts (as in the PREDIMED study) and other plant oils, there is  evidence that heart disease risk will not be increased and may be reduced based on many observational studies.

Trans fats

There is has been a general agreement that trans fats are not healthy. Trans fatty acids also known as partially hydrogenated oils or trans fats (aka bad fat), created in an industrial process that adds hydrogen to liquid vegetable oils to make them more solid, are particular dangerous since they raise bad cholesterol (LDL), lower good cholesterol (HDL) an increase risk for heart attack, sudden death and risk for type 2 diabetes.  Trans fats may be hidden in fried foods like French fries and doughnuts, and baked goods including pastries, pie crusts, biscuits, pizza dough, cookies, crackers, and stick margarines and shortenings. Trans fats increases shelf life and flavor stability of foods containing fats. Compared with other unsaturated oils (non-partially hydrogenated), trans fats are more solid than unsaturated fats but less solid than saturated fats. Trans fats may be either monounsaturated or polyunsaturated oil but are bad for health as a result of the geometry of the double carbon-carbon bond. With the trans configuration, the carbon chain extends from opposite sides of the double bond, rendering a straighter molecule and one with more cardiovascular risk than saturated fats. The Nurses’ Health Study (more than 120,000 female nurses) demonstrated that roughly a doubling of coronary heart disease risk occurred for each 2% increase in trans fat calories consumed (instead of carbohydrate calories) on 14 years of follow-up. Based on a thorough review of the scientific evidence, the U.S. Food and Drug Administration in 2015 finalized its determination that partially hydrogenated oils, the primary dietary source of artificial trans fat in processed foods, are not “generally recognized as safe” or GRAS for use in human food. Food manufacturers will have three years to remove trans fats from processed foods.

Learn more:

Essential Omega-3 and Omega-6 fatty acids

Fat: The Good, the Bad, and the Ugly