High-Quality Fats and Shifting Paradigms Around Fat in Diets

You may be familiar with the idea that fats are perhaps "delicious yet harmful" for most humans, and to be consumed in moderation (see the balanced plate in figure 3.1.1). Recently there has been increased attention focused on the role that "good fats" play in health and development, in addition to the awareness that most diets in more affluent areas of the world contain excessive fat, especially saturated fats of animal origin. Unsaturated fatty acids of plant origin are generally considered essential healthy nutrients, and there is evidence that fatty acids derived from plant sources and fish are important in promoting better neural development and nerve function. For consumers that tend to face food-insecure conditions, also, fats are a highly concentrated energy (calorie) source and therefore a valuable addition to a diet. Where calories are already in excess such as in many urban diets around the world and particularly in the industrialized first world, calorie content is not a benefit of high-fat diets. Recently it has been found that excessively processed or hydrogenated fats often included in processed foods (trans-fats) are harmful to health, and so labeling now specifies the trans-fat content of foods. For example, you can find the trans-fat content of diets in the diet tool used with this module's formative assessment.

Fat in foods as a case study of shifting paradigms in nutrition

(this section is adapted from a contribution by Human Geographer Mark Blumler at Binghamton University)

Most of us have probably absorbed the current overall thinking that fat in diets needs to be treated with caution, that it is synonymous with "divine" or "sinful" food in a joking way, or perhaps that there is something suspect about fat. Because of evolving in limited nutrition environments, most humans are primed to take in fats and other high-calorie foods as a nutritional bonanza and store it away in an evolutionarily "thrifty" way to confront future calorie shortage. However, western nutrition scientists' beliefs regarding different types of fat in diets have undergone drastic fluctuations over the past century (Table 3.1) that may potentially shake our confidence in exactly what is known about "good" and "bad" in nutritional terms. The advice coming out of the nutritional science community, as filtered through government proclamations such as the food pyramid, have also caused enormous changes in the American diet, which have benefited some such as the vegetable oil processing industry, while hurting others such as cattle ranchers and the beef lobby.

To recap this sometimes bewildering history: around the 1960s, scientists discovered a relationship between cholesterol and cardiovascular disease and noticed that saturated fats have more cholesterol than other oils. Consequently, there was a big push to replace butter with margarine and to cut back on consumption of red meats, lard, and other animal fats. Initially, it was believed that polyunsaturated fats such as safflower oil are most heart healthy and so there was a major promotion of such oils. Later, interest developed in the "Mediterranean diet" because of the presence of many very old people in Mediterranean Europe, and nutritionists came to believe that monounsaturated fats such as in olive oil were best for us. Polyunsaturated oils, on the other hand, were increasingly shown to be not beneficial. Meanwhile, further research showed that cholesterol in the blood does not correlate with cholesterol in the diet, undermining the assumption that saturated fats are unhealthy. Trans fats, high in margarine and other processed fatty foods, were shown to be very inimical to heart health. Also, fish oils were recognized as being high in omega 3 fatty acids, which are deficient in the typical American diet today. Recently, butter has been officially accepted as a "good" fat, reversing a half century of denigration of its nutritional value. While other saturated fats are not yet accepted, there is nothing to distinguish butter from the others that would explain how it could be "good" and the others "bad".

It is interesting to compare these shifting attitudes against traditional diets: The Japanese have the longest life span of any nation. Within Japan, the longest lived are Okinawans. On Okinawa the only fat used for cooking is lard (of course, being on an island Okinawans also consume considerable fish oil although they do not cook with it). So, what is going on here? Why can science and scientists not "make up their minds" about fat in diets? Are findings on diet overly influenced by lobbying groups of major food industries, as some have charged for the case of margarine or dairy fats?

The story of fat recommendations illustrates the nature of science, that it proceeds piece by piece, and also seems to have a penchant for identifying single causes that are later shown in the context of a complex system to be overly simplistic. Each research finding, such as that cholesterol is associated with cardiovascular disease, may have been correct. But that gave rise to recommendations that were wrong, because other facts, such as that dietary cholesterol does not correlate with blood cholesterol, were not yet known. Given that many of us would like to eat healthy diets and may also believe that science should guide better nutritional policy, there is a need for principles that emerge from current science to inform dietary recommendations, rather than the confusion that is perhaps caused by this tangled story about the history fats in nutrition. In the summary below, we try to provide some ballpark recommendations regarding fats, other dietary constituents, and lifestyle choices. They summarize many of the same principles from the "balanced plate" at the beginning of this module or the "healthy plate" from the USDA and other nutritional recommendations of government organizations.

Summary: fat consumption within a healthy diet and lifestyle

• Diets very high in fat in the absence of fiber and sufficient fruits, vegetables and whole grains are probably not very healthy within the range of choices of modern consumers.
• Eliminating fats in favor of simple (i.e. non-whole grain) carbohydrates to promote "low-fat dieting approaches" was probably a bad idea.
• Plant-based fats and fish oils, on the whole, seem to contain more health-promoting properties than an exclusive reliance on animal based fat. However, some recent large studies have shown little significant correlation between saturated fat consumption (like those found in meats) and chronic diseases like heart disease, although these diseases are definitely thought of as diet-linked.
• Whole grains of many different types are good, as is a preponderance of fruits and vegetables in the diet.
• Much of this seems to be leading us back towards the principles of more traditional unprocessed food diets without a preponderance of meat (which has benefits for the water use related to a diet as well, as you will see next in module 4 regarding water and food).
• Lifestyles should encompass diet and exercise, but this exercise does not need to be high-intensity for it to have a really positive effect on well-being and health.
• Pay attention to upcoming research and advice from research communities regarding diet, but resist taking them to extremes unless there is robust evidence over the long term, and place them in the context of more traditional knowledge and the other principles we've addressed in this module.