Was milk good for health, or bad for health? Is cholesterol bad? Does that kill or heal red meat? Is the ketogenic diet a godsend or a threat to your health? Can the diet of organic, vegetarian, pescatarian or raw food extend life without disease?
Nutrition is embroidered in many confusions. Why is it so difficult to determine if a meal is good or bad for health?
In medical sciences it is difficult to prove any theory. Nutrition science is no different but it has some unique challenges as well. We outline just a few of those stumbling blocks in this feature.
Despite the many problems faced by nutrition scientists, it is essential to understand which foods benefit or harm the health.
The public is also becoming increasingly interested in finding ways to boost health by dieting. There is now high prevalence of obesity and diabetes, and both have nutritional risk factors. That has further sharpened general interest.
Both fields of scientific research are faced to a greater or lesser degree with the following issues, but because nutrition is so high on people’s minds, the problems appear magnified.
A changing world
Although the water is murky and difficult to cross, major successes have been accomplished in the field of nutrition research. Researchers have known, for example, that vitamin C prevents scurvy, that beriberi grows from a thiamine deficiency, and that vitamin D deficiency causes rickets.
In all these situations there is a relation between a specific compound and a particular disorder. The image, however, is rarely as clear-cut. This is particularly true when researching conditions where multiple factors, such as obesity, osteoporosis, diabetes or heart disease, are at play.
Nutrition-related conditions have also changed over time: deficiencies used to be the most common threats to health, whereas overeating tends to be the primary concern in Western countries today.
Understanding the role of food in health and illness is important and is worthy of attention. In this feature, we’re discussing some of the reasons why nutrition research seems so indecisive, difficult, and straightforwardly confusing.
The ‘perfect’ nutritional study
In an ideal world, an experiment would go something like this to understand the health impact of a given food — goji berries, for example —:
scientists recruit 10,000 participants (both males and females from a variety of nationalities and ethnicities) and house them in a laboratory for 10 years. For the duration of their stay, scientists feed each person the exact same diet, with one difference: Half of the participants sureptitiously consume goji berries — perhaps blended into a mixed fruit smoothie.
For the duration of the study alcohol and tobacco is prohibited.
Participants also have to exercise for the same amount of time each day; if some people do more, they may become healthier, regardless of their intake of goji berry. That’d skew up the data.
Neither the researchers nor the participants are aware of who is receiving the goji berry smoothie; if the participants realized they were getting a “superfood,” the placebo effect could be beneficial. This so-called double-blinding is important when clinical trials are running.
The scientists intensively monitor the wellbeing of the participants during the decade-long study. This could include regular blood tests, as well as medical imaging.
Of course, the form of study’s astronomical cost is the very first stumbling block. Ethics and good sense also suggest this is beyond probability.
In lieu of perfection
Nutritional research has to make some concessions, because the great study is impossible to achieve. So, nutrition scientists are looking in “observational studies” for connections between what a individual eats and their current or future state of health.
Studies of the observation may be incredibly useful. Using this approach, scientists have shown that cigarettes induces cancer in the lung and that exercise is good for us.
Such analysis are far from perfect, however.
The researchers ‘ dependence on self-reported food intake is one problem with observational studies. We are asking participants to note down what we eat for a certain amount of time, or to recall what they ate in the past. That could refer to earlier yesterday or months.
Human memory is far from perfect though. In addition, some people may intentionally miss certain food items, such as their day’s third candy bar. Additionally, participants do not always know, for example, the exact size of their portions, or the complete list of ingredients in restaurants or take-out foods.
Studies frequently ask questions about the long-term health effects of a nutrient component. Researchers, however, prefer to take dietary knowledge only at one or two points in time. In reality, people’s diets over the course of a decade can change significantly.
The issues associated with measuring the intake of nutrients are so ingrained that some authors have called self-reporting a pseudoscience.
The role of industry
These issues prompted a highly critical study to pull apart data from the National Health and Nutrition Examination Survey (NHANES) which appeared in the journal PLOS One.
The NHANES, which began in the 1960s, “is a study program designed to assess the health and nutritional status of adults and children in the United States.”
Experts use the findings to guide public health policy in the United States. The primary method of collecting data for the NHANES is 24-hour dietary recall interviews. Researchers use that information to calculate the intake of energy.
The authors of the important paper conclude that “the ability to predict population trends in caloric intake and produce empirically supported public policy applicable to U.S. food surveillance-related diet-health relationships is extremely limited.”
In an opinion piece, lead author Edward Archer pulls no punches, stating that their paper shows “that about 40 years and many millions of years have passed.” Such findings are commonplace in[…] nutrition epidemiology[…].
Here we meet the industry’s double-edged sword: The PLOS One paper states that funding for the critical study “was provided by The Coca-Cola Company’s unrestricted research grant.”
Company funding certainly does not invalidate the findings of the research, but it should prompt us to wonder what the funder might gain from such research. In this scenario, a company that produces sugar drinks may benefit from destabilizing the confidence of people throughout research that has found their goods unhealthy.
Maybe this case is a bit unusual; more generally, an company with a vested interest would finance studies showing the benefits of a drug.
The California Walnut Commission, for example, regularly funds research which concludes that walnuts are good for us. In the meantime one U.S.- backed study In its abstract the Highbush Blueberry Council proudly states:
“[I]t is widely agreed that the regular consumption of tasty, ripe blueberries can be unconditionally recommended.”
To reiterate, if a study secures sponsorship for the industry, this does not mean people should dismiss the findings out of hand. It should deliver food for thought, though.
Another study in the journal PLOS Medicine examined the impact of research funding by industry on soft drinks, juice, and milk.
The authors conclude, “Industry funding of scientific articles related to nutrition may skew results in favor of sponsors ‘ goods, with potentially significant public health consequences.”
Media outlets prefer to highlight certain results and add to the confusion. For example, if a study funded by a chocolate manufacturer concludes that chocolate prolongs life, media outlets will faithfully reproduce the findings, often without mentioning the funders or a discussion of the limitations of the study.
Diving into complexity
Another problem continuing to haunt work on nutrition is uncertainty. Often, a report may concentrate on the health result of just one particular food component or compound. That can be handled slightly easier.
However, research will often attempt to examine the effects of a given diet. For starters, the Mediterranean diet has gained significant popularity over the last few years.
The challenge here is that the version of the Mediterranean diet of one person might be very different from the version of another. For example, one person might have one small glass of red wine, 25 olives, and an artichoke every day, while another — who may be in the same experimental group of a study— would not drink wine and eat olives or artichoke.
One related issue is that of replacement: For example, if someone does not eat meat, they are likely to replace meat with other protein sources, such as beans or pulses. Thus, when comparing meat-containing diets with those that do not, any health effects may not be due to lack of meat but to the addition of other foods.
Each type of fruit and vegetable contains a vast array of compounds, and their type and quantity can vary depending on where they grow, how they are transported and stored by people, and how they process and cook.
There are so many variables to take into account that it is difficult to determine whether it actually came from the food under investigation even when a study does find a statistically significant result.
Naturally humans are as diverse as the food they eat. Eating a single peanut could provide beneficial nutrients for one person while the same peanut could be fatal for someone with an allergy.
One research from 2015 makes the same point but in a more subtle manner. The scientists continuously assessed blood glucose levels of 800 participants and found “high variation in response to the same meals.”
The authors clarify that this indicates “that uniform dietary recommendations may be of limited utility.”
The scourge of confounding variables
To explain this issue, describing the findings of an imaginary (but not entirely fanciful) study may be helpful: people who eat a lot of spinach live longer than people who do not eat spinach for 5 years.
From that result one may easily conclude that spinach increases the length of life. Nonetheless, it’s worth exploring the alternatives before you head out to stock up.
The extended life span in this case may not be due to the spinach alone; someone who eats a lot of spinach may also eat a lot of other vegetables. In comparison, somebody who doesn’t eat spinach might eat fewer vegetables overall.
Additionally, someone who regularly eats vegetables might have a greater chance of indulging in other safe pastimes, such as exercise. Someone who never eats spinach could be less inclined to work out, maybe.
Of course, these are all theories, but it is clear that other variables are related to the consumption of spinach and these could affect the findings.
Researchers are attempting to “order” certain variables in most studies. Nonetheless, there is always a chance that some unknown factor will alter the findings significantly.
Of course, confounding variables influence all fields of medical science, but since diet and lifestyle are so closely intertwined, they pose a specific threat in nutritional study.
The take-home message
Nutrition is a confounding minefield. It can be a challenge to determine what is healthy and what isn’t. While we can be fairly confident that fruits and vegetables are good for us while there are not high fat, high salt, high sugar products, there are many gray areas there.
One study that brings into strong relief the confusion in nutritional science involves a research literature associated with 50 randomly selected ingredients from the cookbooks. These included pepper, veal, lemon, carrot, lobster, rum, mustard, and raisin.
Of those 50 ingredients, 40 were associated, according to the paper, with either an increase or a decrease in cancer risk. The authors of the study write in their conclusion that”[ m]any single studies highlight implausibly large effects, though weak evidence is.”
So, what can we do? Scientists should continue to improve their methods of study, and add to what we already know. Consumers, the general public and the media outlets all need to be more critical.
In the world of nutrition, in general, there are no quick answers. Because we all need to eat, however, interest is unlikely to vanish and science will continue to forge ahead.