Nutrition information seems to contradict. Advice about what to eat is confusing. Here’s why nutrition science is inconsistent and how to figure out the facts.

Not long ago, experts agreed butter was bad for your health. Researchers had recently figured out that saturated fat, which is the main fatty acid in butter, contributes to heart disease.

Instead of butter, health professionals recommended switching to margarine.

Margarine was a new discovery at the time. Its main fatty acid is an unsaturated fat that has been chemically altered to be more stable at room temperature. At the chemical level, scientists changed a cis bond to a trans bond. Margarine’s main unsaturated fat is trans fat.

Despite this switch from butter to margarine, heart disease rates didn’t improve in the US. Soon researchers discovered that margarine was not only not beneficial, but margarine and the trans fat it contains is actually worse for heart health than butter.

This sort of thing appears to happen all the time with nutrition advice. It seems that health professionals have a confident recommendation, only to change it a few months or years later.

The poor consumers (us) are left wondering what to do and who to believe.

Why does this happen? Why do nutrition professionals seem to change their mind all the time? And why can’t nutrition researchers get it right?

Nutrition Research is Hard to Do

The best type of research is highly controlled. Researchers do this so they can be sure which factor causes the result. Unfortunately, this type of research is very difficult to do with nutrition.

Nutrition is Only One of Many Factors that Contributes to Health

Nutrition – what you eat – is one of the biggest variables that we can control which affects our health.

However, there are lots of other things that also affect your health and risk of disease. There are things we can’t control, like genetics or the air pollution where we live. Factors like sleep, stress, and social connections also have a huge impact on health.

Good research tries to keep as many of these other factors as equal as possible. Unfortunately, that’s not easy to do with human subjects. Real people don’t like to live in a controlled laboratory environment!

Real People Like to Live Their Life (Not Live in a Nutrition Lab)

It’s easy to separate rats into two separate cages and control almost everything. The rats can live in the same environment, eat the same food, and have access to the same water. This makes it easy to introduce just one variable into a research study, like adding a vitamin or controlling access to sugar.

Unfortunately, rats don’t give us good information about human nutrition. Rats and humans break down and use food differently. Animal studies can help researchers ask better questions, but they don’t give us ultimate answers. For that, we need research done in people.

It’s not so easy to separate human subjects into two separate cages.

Real people have families, jobs, and hobbies. When research subjects live in the real world, it’s impossible to control all the other factors that contribute to health.

The Difference Between Nutrition Association and Nutrition Causation

Because it’s very difficult to do highly controlled nutrition studies with human subjects, a lot of the research is done in populations. When lots of people are included a study, it’s easier to sort them into groups to hold most variables constant. This gives researchers the chance to compare the single factor they’re trying to study.

Population research is also called “epidemiologic” research. These types of studies look at large groups of people, separate them into similar groups, and then see which nutrition variables might impact the outcome.

One of the big challenges with epidemiologic research is mistaking association for causation. Let me tell you a story to explain the difference between the two.

Understanding Association in Nutrition Research

A researcher went to a neighborhood. Half of the houses in the neighborhood were blue and half of the houses were green.

After the researcher talked to everyone in the neighborhood, he found out the kids who lived in blue houses were really good at playing basketball. He also found the kids who lived in green houses were really bad at playing basketball.

In research speak, a good scientist would say that living in a blue house is associated with being good at basketball. Living in a green house is associated with being bad at basketball.

“Association” means that two things happen together. It could mean that one thing makes the other happen (causation), but it does not prove that one thing causes the other.

(Mis)Understanding Causation in Nutrition Research

Continuing our story, the researcher concluded that living in a blue house makes you good at playing basketball. He concluded living in a green house makes you bad at playing basketball.

This is an example of mistaking causation for association.

Little did the researcher know that the kids who lived in blue houses had gone to basketball camp that summer. As it turns out, the kids who lived in green houses did not go to camp.

Although it looked like the cause of being good at basketball was living in a blue house, it turned out the real reason was because of another variable that the researcher hadn’t thought about.

Diet Soda: An Example of Mistaking Causation and Association in Nutrition Research

The mistake of confusing causation and association happens often with nutrition information. One of the most well-known examples is the research about artificial sweeteners.

Perhaps you’ve heard that diet drinks cause people to be overweight. This belief comes from population studies which have found that people who drink more diet soda tend to have a higher body weight than people who drink less diet soda.

However, this is an oversimplification that makes the same mistake as the blue vs. green houses example.

The takeaway from this population research is that studies should be done about the effect of artificial sweeteners on hunger hormones and metabolism. But these studies don’t prove causation. It’s important to consider other associations found with diet soda and weight, because these might be the cause of higher body weight rather than the diet soda itself.

These other associations have been found with diet soda and weight, which might explain the difference:

  • People who drink diet sodas tend to have other less healthy behaviors (exercise? drink less water?)
  • We feel good about saving calories on diet instead of regular, so we splurge on other high-calorie foods
  • Diet soda pairs really well with French fries and other high-calorie, low-nutrient dense foods

Drinking a diet soda will not cause you to gain weight directly. Instead, you may want to notice the patterns that emerge when you drink diet soda consistently.

Good Nutrition Research Takes a Long Time

If researchers can’t do controlled studies of individual people and the epidemiologic research can lead to misunderstanding, how do we know anything about nutrition at all??

The short answer is boring: good nutrition research takes lots of time and repeated studies.

The Best Nutrition Research Includes Lots of People Over a Long Time

There is a type of population-based research that is done over time. These are called “prospective” studies and are much better than looking at a group of people at one point of time only.

Lucky for me as an evidenced-based dietitian, there are a lot of good research studies out there. These quality studies are household names among my dietitian friends. They include studies like the Nurses’ Health Study, Adventist Health Studies, and the Health Professionals Follow-up Study, among others.

I use these types of research when I review popular diets like these:

Misunderstanding #3: One New Research Study Finding Does NOT Debunk All Current Standing Knowledge

Each new research study that comes out adds to our knowledge. A study that contradicts the findings of one of the large population studies doesn’t not “prove” that large study wrong. Instead, a good scientist uses that contradictory study to ask more questions.

It takes a long, long time before nutrition recommendations are changed because it takes many repeated, quality studies to make sure the contradictory results weren’t just a fluke.

Good Nutrition Advice Changes with New Information

The butter vs. margarine debate is a great example of learning new information and adjusting recommendations accordingly.

Here are some things we’ve learned about fat since the original recommendations to reduce fat in the diet came out:

  • Not all fat is created equal. Some fat promotes heart health and other fat increase the risk of heart disease.
  • Not all unsaturated fats have the same effect on health. Omega-3 and mono-unsaturated fats are heart-healthy. Omega-6 fatty acids are healthy in small amounts and detrimental when consumed in excess. Trans unsaturated fats are disease promoting.
  • There are different types of saturated fat. Longer chain saturated fatty acids seem to have a negative impact on heart health while medium chain saturated fatty acids may be closer to neutral.
  • Replacing fat with simple carbohydrates in the diet does not improve heart health. If someone lowers their fat intake, it’s very important to replace those calories with nutrient-dense foods like fruits, vegetables, and whole grains. Replacing them with refined sugar and flour can increase the risk of heart disease.

Because of these new discoveries about fat, the guidelines have changed over time. Instead of simply instructing someone to decrease the amount of fat they eat, I work with my clients to use heart-healthy fats primarily and enjoy other fat in moderation.

How to Figure Out the Truth when Nutrition Advice Contradicts Itself

It’s easy (and normal) to feel overwhelmed by the 30 billion search results Google responds with to your nutrition question.

Instead of trying to learn everything about nutrition – unless you want to get a Master’s degree – I recommend to find an expert you trust and talk to them. Follow these steps to identify credible nutrition information when you go about searching for that expert.

A registered dietitian nutritionist is a good place to start when looking for an expert in nutrition. The person you talk to should be able to discuss the nuances of nutrition science. More importantly, they should be able to tailor their nutrition recommendations for you specifically – not just give you a “one size fits all” diet plan.

If you meet someone or read something online who has all the answers in an easy black-and-white formula, beware. As the philosopher Bertrand Russell so wisely stated, “…fools and fanatics are always so certain of themselves, and wiser people so full of doubts.”

Nutrition information seems confusing because the question is complex. That’s why I love what I do: help make healthy eating easier for busy families.

Sharing the Truth about Nutrition Information

If this information has helped you understand why nutrition advice is so confusing, I would be honored if you shared this article with your network. You can share it and tag me on Instagram, Facebook, TikTok, Pinterest, or LinkedIn.

There is a lot of misinformation out there. Help me share the truth so more people can love good food.

Because, as my motto states, Life’s too short for bad food!

Happy nutrition truth finding,
Dietitian Ann from Peas and Hoppiness

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