pellagra and beriberi epidemics appeared for the first time. In pellagra, the parts of the body exposed to sunlight suffer from dermatitis, but there are also mental and gastrointestinal implications. Using epidemiologic methods, scientists determined that pellagra was a disease of nutritional deficiency common in people who obtain most of their food energy from maize, notably rural South America, where maize is a staple food.
FIGURE 5.1 Perifollicular hemorrhages on both legs (a) and ecchymosis (b) are classic skin findings of scurvy.
Source: Reprinted from Lipner (2018): 431.
There are two types of beriberi – wet beriberi, which affects the cardiovascular system, and dry beriberi, which affects the nervous system. Around 1937, scientists detected that the lack of niacin (vitamin B3) and thiamin (vitamin B1) caused pellagra and beriberi, respectively.
In the last few decades, newly discovered food constituents have been shown to affect human health. For example, there is now considerable scientific evidence suggesting that plant polyphenols, which belong to the large group of phytochemicals, may account for some of the reported anti‐carcinogenic and cardioprotective effects of plant foods. On the other hand, polyphenols, like flavonoids and lignans, have been associated with decreased risk for the development of CVDs. Two other polyphenolic classes, flavonols and flavones, have been shown to decrease mortality rate and prevent fatal and nonfatal coronary artery disease.
Even though it is now generally accepted that several nutrients have positive health effects, people do not consume single nutrients; they consume foods. And foods consist of many different nutrients in heterogeneous proportions.
Foods and Food Groups
Diseases caused by specific nutrient deficiencies usually manifest soon after initiating the nutrient‐deficient diet and can be reversed within days or weeks after replacing the specific nutrient(s). However, the degenerative chronic diseases are not just a matter of nutrient deficiencies; their development is contingent on a constellation of risk factors, and they are characterized by heterogeneity and complexity. The interplay between human metabolism and all of the compounds found in foods of plant or animal origin create an intricate nexus of interactions, rendering the isolation of a single effect difficult and possibly misleading.
This notion triggered scientists to speculate that food components interact with the food matrix in which they are found, developing additive or even antagonistic effects on human metabolism and, by extension, on human health. This combined effect is defined as food synergy and food antagonism, respectively. Therefore, provided that the individual components of a food interact with each other and have a paired influence on health, questions began to emerge as to which is the best way to assess the overall impact of food consumption on health and disease. As a consequence, a new approach developed, that of the impact of whole foods and food groups on specific pathologies. For example, the increased consumption of whole‐grain products has been shown to lower the risk for developing CVDs, T2DM, and some types of cancer. Whole‐grain products are rich in several bioactive micronutrients and macronutrients with various health benefits; many of these beneficial micro‐ and macronutrients are lost during refining of the whole‐grain product. Other food groups with high concentrations of nutrients and non‐nutrients with advantageous influence on health are fruits, vegetables, and legumes.
Another important point to consider is that the health effects of foods depend on the biological properties that their nutrients maintain after digestion and not on the properties that they had before they were ingested. For example, although phytochemicals have been attributed advantageous effects against CVD, a study conducted in Welsh men, a population known for increased consumption of tea rich in flavonols, failed to detect such an effect. The researchers speculated that by adding milk to the tea, the flavonols could not be absorbed sufficiently, and therefore, this cohort of Welsh men did not benefit from the favorable effects of the tea flavanols. Another example of food antagonism is that of the inhibition of zinc absorption when iron is present. On the other hand, vitamin C enhances the absorption of plant‐derived iron, i.e., nonheme iron.
Moreover, for many years, eggs were thought to increase the risk for the development of CVD, due to their high cholesterol content. However, the available evidence so far does not support the notion that dietary cholesterol increases the risk of heart disease in healthy individuals. Indeed, the effect of egg consumption, up to seven a week, on blood cholesterol is minimal, especially when compared with the effect of saturated fatty acids on blood cholesterol. Dietary cholesterol is common in foods that are high in saturated fatty acids, and this might have contributed to the notion that dietary cholesterol is atherogenic. Focusing only on the cholesterol content of eggs, without taking into consideration the fact that eggs are also a rich source of amino acids, vitamins, minerals, and other nutrients, may negatively influence the quality of our diet. It is obvious that our knowledge of the relationship between dietary cholesterol and cardiovascular disease in patients with diabetes is still incomplete. Therefore, further research is needed.
Key Point
The health effects of foods depend on the biological properties that their nutrients maintain after digestion and not on the properties that they had before they were ingested.
Holistic Approach to Diet; Dietary Patterns
Humans consume complex combinations of foods in the context of their meals, rather than individual foods or food groups. This is why it makes even more sense to assess dietary patterns rather than the effect of certain foods or even food groups. Dietary patterns can be described as the type, quantity, quality, frequency, and proportions of foods and drinks that are consumed by a particular population in a specific geographic region. Dietary patterns have developed over the centuries and have been influenced by environmental factors such as climate, terrain, and geography and cultural factors such as tradition and religion.
There are many different dietary patterns around the world that reflect the dietary habits of the populations that have adopted them. The main dietary patterns that have been scientifically studied so far will be presented in the following chapters of the book. The various dietary patterns can be classified into the following categories: (i) those describing the dietary habits of whole populations residing in a specific geographic area (e.g., Mediterranean diet, Asian diet); (ii) those that have been shown to be healthy through epidemiological studies (e.g., the Prudent Dietary Pattern); (iii) those developed to serve certain health goals (e.g., the Dietary Approaches to Stop Hypertension [DASH] and the Therapeutic Lifestyle Changes [TLC] diet); and (iv) those created to be consistent with certain moral principles (e.g., vegetarian diet).
Key Point
Humans consume complex combinations of foods in the context of their meals, rather than individual foods or food groups.
A dietary pattern is categorized as “healthy” by either (i) an a priori‐defined healthy diet quality score/index based on the existing dietary guidelines; or (ii) a posteriori‐derived healthy dietary pattern based on variations in food intake, developed using principal component analysis (PCA).
An example of a well‐known dietary quality score/index is the Healthy Eating Index (HEI), originally published in 1995 to evaluate the extent to which Americans are following the dietary recommendations. Since then, the HEI index has been revised several times. The index
