Every week we’re inundated with information telling us what to eat, what not to eat and when to eat it. Do we focus our diet to aim for macronutrients, calories or food patterns? New studies come out either telling us what we know or that we’ve had it wrong all this time, while others seem to go around in circles telling us what was once good is bad and vice versa. It makes it hard to figure out what a good diet is, let alone an ideal diet.

A perfect example is the egg. Studies on eggs have gone back and forth for decades from saying eggs are fine, to saying they increase one’s chances for heart disease and early death. And a 2020 study reported people with higher egg intake were more likely to get type 2 diabetes.

If we add in commercial motives of the food industry it gets even more confusing. From the sugar industry funding studies to make dietary fat look bad to nonsensical marketing (what is gluten-free water anyway?) to product placement on grocery store shelves (there’s a reason why sugary cereals are on the lower and middle selves of grocery stores), and it’s enough to make us give up. It’s not that scientists are trying to pull the wool over everybody’s heads. It’s just that studying nutrition is extremely difficult.

We Need Food to Live

Probably the number one complexity is that we can’t change the fact we need food to live. It’s not like smoking in which the ideal number of cigarettes smoked is zero. So we can’t just tell people what not to eat (which unfortunately happens). We need to also advise people on what to eat.

Most nutrition studies focus on a specific food (such as eggs) or nutrient (such as fat). For example, a higher intake of fish is associated with a lower risk of heart disease. But does it? When people eat fish, they may be eating less of something else to accommodate it (most often people eat less red meat when eating fish). So is it eating the fish that’s good, or not eating something else, or a bit of both?

Another example being debated right now is whether saturated fats are all that bad for you. Some studies saying they aren’t as bad as we thought. But really, it matters what we replace the fat with that’s just as important. If someone reduces their saturated fat and replaces it with sugars, this is likely a poor health change. However, if saturated fat is replaced with unsaturated fat, this could be a healthier choice.

The reality, however, is that our diet is not just a single food or nutrient in isolation. We need, and eat, a variety of foods to live and thrive. We can’t survive for very long on any one type of food.

How much food am I eating?

Another issue is the difficulty in knowing exactly what a person eats. Of course the most common method is to ask people what they ate. And generally people are pretty good in knowing what they ate. But not so great at how much. Last night our family had hamburgers for dinner; mine had cheese, lettuce, tomatoes, cucumber and ketchup and my son’s had cheese, ketchup and BBQ sauce. But quite often people just report they had a hamburger. It’s also hard to know how much a person ate. Most people underestimate their food intake. In the morning I had a bowl of cereal, but I don’t know what size it is.

Some researchers ask participants to measure out their food, which can help. Although the act of measuring out foods may actually change how much a person eats. Usually people measuring their food eat less, or even avoid foods out of not wanting to have to measure them. The dilemma in nutrition research is that the more accurate we get in measuring a person’s usual diet (using measuring cups, scales, portion samples), the more likely they are to change their diet. Technology, such as taking photos using mobile phones, may make it easier and more accurate to capture what people eat.

Another challenge is how nutrition studies are conducted. The most common method is what’s called an observational study. In these studies, people report their eating habits at a point in time (usually using one of the methods mentioned above) and then followed for a number of years. However, behaviours such as diet do change over the years. A 2019 study in which eggs were associated with higher chances of getting heart disease and early death 17 years later was highly criticized for this weakness. A more robust assessment would have been to measure diet at various points during the follow-up.

Diet Intervention Studies

Conducting a dietary intervention study that requires people to change what they are eating is equally if not more challenging. Compared to observational dietary studies, there are very few studies which prescribe people to on diet or another. The Lyon Heart Study did so by investigating the effect of the Mediterranean diet early death in people with heart disease.

But these studies are immensely difficult to conduct, and are more costly and resource intensive than the typical medication/placebo trail. Most often the new diet is provided through dietary counselling to participants. Participants still need to purchase and prepare the foods themselves. Sometimes researchers will provide participants with foods, which can help minimize these barriers. But adherence to the intervention diet is always a challenge.

So what is the ideal diet?

It is unlikely that science will ever provide the answer to: What is the ideal diet? There are too many factors to consider. From how foods are produced and processed, to combinations of various foods eaten together (do foods act differently in certain combinations?). Not to mention the fact we are all individuals and what may be ideal for one person, may not be for another.

Despite the possible confusing and contradictory diet and nutrition advice, life expectancies around the globe continue to increase and a key reason for that is increased access to healthy foods. Even though we aren’t all nutrition scientists, we do have a pretty good understanding of what are healthy foods and our bodies are pretty good at metabolizing the foods we eat. At times, though, it’s not always easy to stick to what we know as a healthy diet.

Where nutrition science comes in, regarding individual diet and nutrition, is it can help to delay the onset of disease and potentially add a few more quality years to our life that might not otherwise happen. This is a good thing, and we need to encourage health care professionals and scientists to provide this information in a way that is scientifically rigorous and easily digestible (bad pun!).

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This post was originally published on November 29, 2017 and updated on March 3, 2021.