Fat Myth: Do we really have STRONG evidence to recommend reducing saturated fat as the proposed USD
From the 50s of the last century, we have been told that saturated fat is harmful and we should reduce it in our diet to make it healthier. When Dwight Eisenhower got a left anterior myocardial infarction in 1955 while visiting his in laws in Denver, his doctors treated him with heparin, low fat diet and asked him to keep his weight at 175 lbs. However his unexpected heart attack sent a shocking signal to the entire nation indicating that no one is immune from a sudden and frequently lethal heart attack. This unwelcomed event may struck without warning whether on a beach or at a movie theater. At that time, it was easy to blame the American diet particularly the high fat consumption for the increased cardiac risk. At that time, there was nothing else to blame including smoking.
In 1977, the Select Committee on Nutrition and Human Needs of the US congress solidified these recommendations, despite scarce data that link increased fat consumption to coronary artery disease, by urging Americans to reduce fat consumption especially saturated fat and cholesterol. Based on the committee recommendations, the USDA asked the entire nation to cut saturated fat to <10% of the total caloric intake and to reduce cholesterol to <300 mg/day and to reduce total fat consumption from 40% down to 30% of the total daily calories. After almost 40 years, we discovered that 2 of the three recommendation, total fat and cholesterol, were wrong! The USDA is now admitting those mistakes in the proposed 2015 guidelines. What about the third one? The 1977 congressional committee chairman and later presidential candidate, George McGovern, stated that “too much fat, too much sugar or salt, can be and are linked directly to heart disease, cancer, obesity and stroke, among other killer diseases. In all, six of the ten leading causes of death in the United States have been linked to our diet”. His bold statement opened the gate for many dietary changes including that one on fat. Interestingly, every guidelines since that time, including the proposed dietary guidelines of 2015 continued to follow the same pattern of recommendations; citing that there are STRONG evidence to link increased saturated fat intake to high serum LDL-cholesterol and increased risk of cardiovascular disease and mortality. Although the proposed guidelines removed the upper limit on total fat intake ignored cholesterol, which are an overdue movements, they continued to keep a cap on the upper limit of saturated fat intake at no more than 10%. They also continued to recommend low-fat or no-fat dairy products. I'm afraid that the public have to accept these guidelines without having any chance to challenge them or even ask about the credibility of the STRONG evidence that support them. Our understanding is that STRONG evidence refer to evidence that are consistent over time, solid without any doubt and are unlikely to change in the future. We have the right to ask: is it the case with the proposed saturated fat recommendations? Are we forced again to continue the national nutrition experiment that started in the 70s of the last century until we realize that we made several mistakes and remove them one by one; the recommendation that up till now did not decrease the incidence of obesity, type 2 diabetes or coronary artery disease and in contrary increased them? Everyone in the medical community knows that the reduction in the cardiovascular events over the last decade is related to statin use and not to our dietary pattern.
Most people don't know that there is no food in nature contains pure saturated fat. For example, chicken fat has more unsaturated fat than saturated fat and beef fat has equal amount of saturated and unsaturated fat, while most oils except tropical oils have more unsaturated fat than saturated fat. Currently, US population are eating less saturated fat and more polyunsaturated fat than their peers in Europe. We are also eating less cholesterol than them. This means that we are consuming the type and amount of fat that we were told to eat since 1980. You can realize that by looking at the dairy corner of any grocery store. You will immediately notice that the majority of food products are either reduced in fat or contain no fat. The logic question is: are we healthier than the Europeans? Do we have less obesity and type 2 diabetes than France and Germany, which consume more fat and even smoke more than us? Before implementing any new guidelines and repeat the same mistakes, we should ask ourselves: are we really have STRONG evidence to link higher intake of saturated fat to coronary artery disease and stroke? Are all saturated fat created the same?
Siri-Tarino et al in 2010 showed, in their meta-analysis of 21 prospective studies, which included 347,747 subjects for a duration of 5-23 years of follow-up, no relationship between saturated fat intake and coronary heart. Their study also found no relationship between saturated fat intake and stroke. Similar observations were seen in the Zutphen study in 1984 and the Health Professional Follow-up study, which followed 43,757 health professionals aged 40 to 75 years for 6 years and published in 1996. Again the same observation was seen in the ATBC study in 1997, which included a prospective cohort of 21,930 smoking men aged 50-69 years and followed them for 6.1 years. Meta-analysis of prospective and randomized trials done by Skeaff CM and Miller J in 2009, confirmed the same observation in a cohort that has a median saturated fat intake between 9-20%. Another proof came from the meta-analysis done by Mente A et al on the same year that included 223 prospective cohorts and 66 randomized controlled trial. More recently in 2013, O'sullivan TA et al. in another meta-analysis of 26 studies also did not find any relation between saturated fat intake and cardiovascular disease mortality. In reality, there are more studies to show no relationship than studies that suggest relationship between saturated fat intake and cardiovascular mortality. The later includes the controversial Seven Countries Study in 1980, the Honolulu Heart Program in 1985, the Israeli Ischemic Heart Disease Study in 1993 and the Nurses' Health Study in 1997 and 1999. However, since 2009 four major meta-analyses of prospective and observational studies found no relationship between saturated fat and cardiovascular mortality. My argument is that if we accept that the studies that support this relationship are in balance with the studies that don't support this relationship, there is no way for us or the USDA to say there are STRONG evidence to link increased saturated fat intake to coronary heart disease mortality unless we totally ignore the clear side of the coin.
The major pitfall is that everyone assumed that since saturated fat increases LDL-cholesterol, which is known to be linked to cardiovascular, then saturated fat would indirectly increases risk for cardiovascular disease. However, studies that evaluated the direct relationship between the two did not confirm this association. It is likely because saturated fat also increases the cardio-protective HDL-cholesterol; a factor that is frequently ignored in such interpretations. Meanwhile, saturated fat increases the mass of large LDL particles and LDL peak particle diameter and flotation rate, which mean that it converts the atherogenic pattern B of LDL-cholesterol (small dense LDL) to the non-atherogenic pattern B of LDL-cholesterol (large-fluffy LDL) as shown in a study done by Dreon DM et al in 1998.
The source of saturated fat also makes a big difference. Saturated fat from meat and processed meat may be associated with a slight increase in the risk of cardiovascular mortality as shown in O'Sullivan TA et al meta-analysis in 2013. However, saturated fat from all dairy products and in particular milk and cheese was not associated with increased cardiovascular mortality. Meta-analysis of 6 cohorts also showed that dairy products were associated with reduced risk for type 2 diabetes. A meta-analysis of 4 prospective cohorts showed no relation between increased milk consumption and cardiovascular disease, however a meta-analysis of 6 prospective cohorts showed that increased milk consumption was associated with reduced risk for stroke. The proposed guidelines also demonstrated that Americans have nutritional deficiency in vitamins A, D and E, but did not tell the public that all the three vitamins are fat soluble and need dietary fat to be absorbed. In another word, fortifying milk with vitamin D is basically useless if the milk is skimmed, since absorption of vitamin D will be impaired due to absence of fat in skimmed milk. It make sense to ask people to increase monounsaturated fat such that present in olive oil, canola oil and avocado, or to ask them to trade saturated fat for monounsaturated fat since we all agree about the health benefits of such fat as shown in the studies done with the Mediterranean diet plan. But if we are asking the public to trade saturated fat for polyunsaturated fat, as the expert panel suggests, we have to tell them that few studies showed that this type of fat, which is mostly found in plant oils like corn, sunflower and vegetable oils, is associated with increased risk of some types of cancers like prostate and breast cancers, increased level of oxidized LDL-cholesterol, which is atherogenic, and reduced serum HDL-cholesterol, which is also atherogenic. Although evidence for these harms are not strong, these signals are alarming.
I think we have to seriously go back and look again to the scientific evidence behind the new recommendations on fat and challenge them in order not to repeat the same mistakes over and over again. We, as nation, suffered from wrong dietary recommendations in the 80s when the USDA put carbohydrates at the base of the dietary pyramids. As a physician and a clinical researcher in obesity, diabetes and nutrition, I don’t need to wait for another 40 years until we realize that we were wrong again about saturated fat. I don’t think I’m ready to give up my whole cream cheese, milk or yogurt, which were graciously offered by nature. I find it hard to believe in the fat myth that was created and ballooned over years based on unfair look to scientific evidence that we still call it STRONG.
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