Diet is the food we consume and nutrition is what it provides in terms of nourishment to the body. Nutrition is clearly fundamental to health, wellness and longevity. This is conventional wisdom that everyone acquires as they grow up and are reminded of by parents and teachers. If anyone has not already registered the message, media features and industry advertising saturate us with messaging on what to eat and what to avoid to stay healthy or grow healthier. Everyone espouses the vital role of good nutrition at every stage of life.
It is nutrition that builds our body, whether it is blood, bone, brain or muscle. It helps in making hormones and building immunity. It enables reproduction. When nutrition goes awry, inflammatory processes can get activated to damage many parts of our body, increase the clotting tendency in the blood or block blood vessels to cut off the supply to the heart or brain. An unbalanced diet leads to general or abdominal obesity, both of which are associated with increased inflammation, heart disease, diabetes and risk of cancer. Nutrition is not just the fuel that gives us the energy to lead our daily lives. It creates and nurtures the very fabric of our existence, the whole human body.
Confusions and contradictions
It is a big challenge to understand how we can acquire good health through our daily diets. This is where consensus breaks down, within the scientific community, the food industry, popular belief and media messaging. This results in confusion and contradictions, which leaves the common person bewildered most of the time and often cynical about dietary advice. It does not help that serious scientific positions as well as media enthusiasm for fad diets change frequently.
Much of the confusion arises from a reductionist approach to scientific enquiry. There is a widely prevalent credo among researchers that attribution of benefit or harm is possible only when individual nutrients are studied in isolation or specific food items are assessed. This is usually done through long-term follow-up of some population groups or through randomised controlled trials of dietary interventions. Comparison of different populations helps in identifying why certain diets may be healthier than others but such ecological comparisons are vulnerable to confounding or distortions by many other factors that may be operating at the population level. So, such studies are thought to be hypothesis generating rather than hypothesis testing.
The molecular ‘problem’
Nutrition scientists were happiest to begin by pursuing a reductionist approach, breaking down diets to the molecular level. Not just the effect of carbohydrates, and fats as a class but the specific effect of every nutrient in each class. Of course, it is good to know that from the point of view of understanding the physiological effects of each nutrient. However, such knowledge is not always helpful in predicting how the body behaves when that nutrient is added, enhanced, reduced or eliminated from the diet. So also with individual food items.
That is because diets are composed of many food items, each with many nutrients. They balance, supplement, enhance, diminish or counteract each other’s effects on the different body systems. A reductionist approach to studying isolated nutrients or single food items does not provide adequate evidence of how the human body responds to them when consumed with other nutrients or food items.
The value of antioxidants
To understand this, let us look at the popular discussion of the value of antioxidants on human health. These are nutrients like Vitamin E, beta-carotene and Vitamin C. Long-term follow-up studies of population cohorts suggested that foods containing these antioxidants were protective against heart disease, cancer and some other disorders associated with high oxidative stress. The industry decided to market individual antioxidants or combinations thereof with gusto, packing them in pills and pouches instead of natural foods.
Other scientists set out to evaluate the protective effects of individual antioxidants on disease outcomes through randomised controlled clinical trials that are less susceptible to methodological bias than cohort studies. In most cases, the antioxidant supplements conferred no benefit. In some cases, they actually caused harm. So, does this debunk the protective value of antioxidant vitamins? There can be several explanations for these contradictions. The observational cohort studies may indeed have been biased. The doses administered may have been inappropriate. The pills taken at one meal may not have retained the blood levels to counter the oxidative stress related to other meals. The synthetic chemicals in the pills may have been different isomers of natural vitamins, with less effect.
More likely, the many phytonutrients in fruit and vegetables, the natural sources of these antioxidants, would have had potentiating interactions that the isolated synthetic vitamins would not have. Natural fruits and vegetables are power-packed with hundreds of phytonutrients like vitamins, minerals, flavonoids and fibre, which act in concert. They contain potassium that balances the effect of dietary sodium, lowers raised blood pressure and reduces the risk of strokes. The protective role of fruits and vegetables against heart disease and cancer has been corroborated by several later cohort studies and clinical trials too. Reductionism lost that round. Score one for Nature!
And then the fish!
Similar debates continue to be waged around food items like fish. The problem arises when fish oils are put into a capsule for conducting trials. The differential effects of the two main fish oils (eicosa pentaenoicacid or EPA and docosa hexaenoic acid or DHA) together modulate the biological effects in the body but clinical trials that use different ratios of these come up with different results when evaluating the impact on vascular events or heart rhythm abnormalities.
Yet again, the capsule is a distraction from the nutritious value of the natural fish diet. Also, extrapolating from the composition of a single food item its physiological effects on the body, based on a single nutrient in its composition, has proved inaccurate and even counterproductive as in the case of nuts and eggs.
The single-food item issue has been a problem in many other cases too. Take butter versus margarine. For several years butter was banished because of saturated fat content and margarine was feted. However, the finding that trans-fats in margarine were far more dangerous than the saturated fat in butter dethroned the pretender. The manner in which the food item is prepared or consumed is also not often taken into account in research studies. Was the meat smoked or salted? Did the fruit lose its fibre and liberate free sugars in its extracted juice? Were the vegetables sautéed, fried or boiled till the nutrients leeched out?
Focus on composite diets
Such contradictions and controversies, which abound in reductionist research on individual nutrients and solitary food items, have led to researchers asking whether it is the total composition of the diet, that is far more predictive of health outcomes. The interest was stoked by evidence of longevity and good health conferred by the Mediterranean diet and the Okinawa diet as well as the composite DASH diet, which was trialled for the treatment of hypertension.
A major finding of studies conducted on several of the composite diets is that the dietary pattern is what is beneficial and not any individual component. This has been clearly demonstrated in studies of the Mediterranean diet that struggled to find a single component (such as olive oil) to which the protective effect could be attributed.
However, as the score increased of the nine identified components of the Mediterranean diet, the protective effect rose! This is what scientists call a ‘dose−response’ relationship. What this finding demonstrates is that a reductionist lens fails to detect the health benefits of a composite diet.
It is not necessary that the whole world should adopt the Mediterranean diet. Local cuisines can adopt the principles of a healthy composite diet, combining easily accessible and relatively inexpensive ingredients. Harvard researchers assessed the health outcomes of a ‘prudent’ diet and a ‘Western diet’. The former is characterised by a higher intake of fruits, vegetables, legumes, whole grains and fish. The latter consists of red and processed meats, refined grains, sweets and desserts. Ultra-processed foods dominate harmful diets, while natural foods are plentiful in a prudent diet.
These principles can be used to promote prudent diets appropriate to each cultural, climatic and economic context.
Four legs of the dining table
The key guiding principles of a healthy dietary habit are like the four legs of the dining table. They are variety, balance, moderation and regularity. These are the legs on which a health-promoting diet will need to stand. Dietary diversity is key to good nutrition and provides balance while enhancing enjoyment. A prudent diet, created and consumed based on these principles, will help to make and maintain good health over the life course. Predominantly plant-based diets are best suited for human health as well as ecological sustainability. As we move from the reductionist paradigm of looking at nutrients in isolation, we can also embrace the holistic vision of creating food systems that can protect the planet, which gifts us life-sustaining nutrition.
Excerpted with permission from Pulse to Planet: The Long Lifeline of Human Health published by HarperCollins.
(The author was the head of cardiology at the All India Institute of Medical Sciences, Delhi, before establishing the Public Health Foundation of India. He is presently an Adjunct Professor at Harvard, Emory, Pennsylvania and Sydney universities.)
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