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Evidence in nutrition

Nutrition Sciences is a relatively young discipline^[1]. There is much debate about what is healthy and which metric is best for measuring health. When we consider the structures around weight and dieting, studying human health has as many social implications as it does scientific. In this chapter, we take an interdisciplinary approach to addressing issues of evidence in relation to nutrition, dieting, obesity and health. To best understand not only the evidence itself, but also the way people engage with it, we include nutrition science, sociology, communications and economics in our discussion of these issues.

Research in Nutrition Science

Modern nutrition science began in the early 20th century with the supplementation of food with vitamins, which led to a decrease in deficiency related diseases. In wealthy countries, the discipline then became focused on dietary fat and sugar as posing health risks. In 1977 the US Senate Committee on Nutrition and Human Needs published a somewhat controversial report titled Dietary Goals for the United States that recommended a low fat diet. The evidence used in this report was called into question and found insufficient by the US National Academy of Sciences, Food and Nutrition Board. ^[1]

Methodologies

Data in nutrition sciences are gathered in many ways, ranging from ecological case studies, to intervention experiments. The methodology used to address deficiency diseases, which involved isolating a nutrient, was applied to research on the impacts of sugar and fat in the 1950s-70s. However, these methods, while effective for their original purpose, were not well suited to non-communicable diseases like obesity^[1]. Researchers today still use a lot of the same methods, but hold their data to a much higher standard of accuracy. Additionally, more recent publications are less likely to make far reaching claims about the relative health of different foods.

Funding and Biases

The rise of the internet has given the general population access to a wide variety of studies, articles and arguments regarding health; however, the evidence presented in these sources may not always be legitimate. This applies even to studies that appear to be academic, when we consider research sponsorship. There have been multiple cases in which the outcome of a study has favoured the interests of the funding body.^[2] For example, the Coca-Cola Company conducted research to show that exercise is more important to one’s health than nutrition.^[3]

Media outlets, such as the Guardian and Inside Philanthropy, have drawn attention to the issue of corporate influence in academic research. It has also garnered attention from academics, such as Dr. Dariush Mozaffarian of Tufts University, who recently published this study on conflict of interest in nutrition research. He concludes that “evidence for substantial bias has been identified in conclusions of industry- sponsored systematic reviews regarding the health effects of sugar-sweetened beverages and artificial sweeteners.”^[4]

The presence of food industry capital in research is enormous, and is closely linked to the industry’s presence in national health groups in countries like the USA^[5]. These findings call into question the validity of the evidence for health and nutrition.

Health

The official definition of health, given by the World Health Organization (WHO) in 1948, states that "health is a state of complete physical, mental and social well-being and not merely the absence of disease of infirmity." ^[6] WHO fails to indicate how the subject is produced or measured.^[7] Similarly, the OED and the NHS provide scarce explanations of health. An article from the British Journal of General Practice^[7] defines ‘health’ as the capacity to make an adaptation to an environment, and is subject to a variety of forces that can change and damage us. ^[7] There is not only conflict over how we define health, but how to achieve that state. There is a large body of research and evidence, leading to little concrete conclusions.

Obesity and Related Diseases

There is extensive scientific research that suggests obesity is linked to problems with health, including cardiovascular diseases and Type II diabetes.^{[11] [12]} The evidence regarding these findings is rather uncontroversial and accepted by both the scientific community and general population. Issues of evidence become more important in defining obesity. According to the World Health Organization (WHO), “Overweight and obesity are defined as abnormal or excessive fat accumulation that may impair health.”^[6] There are multiple metrics used to measure obesity, including Body Mass Index (BMI) and percent body fat.

As stated in the introduction, evidence in nutrition is not just a scientific issue, it is also something we engage with on a social level. Society places high value on thinness, which impacts the general perception of health. If someone appears thin or "in shape" this is often taken as evidence of their good health. However, even people with normal BMIs can have what professionals call "normal weight obesity," which is also correlated with increased risk of cardiovascular disease and other health problems.^[13]

Advertising

Cambridge Dictionary defines advertising as “the business of trying to persuade consumers to buy given goods or services.” ^[14] In order to achieve this end, advertisers must provide reasons, or evidence, to support their product. The main issue in diet advertising is the manipulation of data or inaccurate paraphrasing of scientific findings. So called “soft” health claims, such as “makes you healthy” are intentionally vague, resulting in their interpretation as valid health claims.^[15] According to M. Katan, ¨the formulation of soft claims [is] a fine art, creating claims that imply health effects without actually naming a disease¨^[16] The issue of evidence in diet advertising in important not only because of the link between diet and health, but also because advertising is a dominant tool in shaping health preferences and knowledge about food. This especially impacts children and teenagers, as they are the most vulnerable to external influence.^[15]

Some evidence suggests that food marketing practices may have led to positive public health outcomes, by changing dietary habits among American customers. ^{[17] [18] [19]} For instance, there has been a trend away from high-fat foods since the 1970s. ^[18] Additionally, a report from the American Marketing Association argues that health claims in advertising can transform markets.^[20] Allowing truthful claims by manufacturers may benefit consumers, as it increases the competitive pressures on companies to market the nutritional features of foods.^[18] Health claims can also be seen as a legitimate educational tool.^[15]

On the other hand, many argue that health claims in advertisements are “designed to deceive,” by withholding some scientific evidence.^[21] One study found that most advertisements promote “energy-dense, nutrient-poor” food, which has a questionable health benefit.^[22] There is also a link between the proliferation of health claims, and the change of nutritional public policy. These claims are commonly found on food products throughout the world, but their regulation varies widely among countries. A recent WHO survey reported that among 74 countries, 35 have no regulation on health claims. ^[23]

Evidence is important in making and defending arguments about the value of health claims, yet it does not definitively support either side of the debate. This subjective and inconclusive nature of evidence has impacts on our health, policy and society as a whole.