Here’s What You Should Know to Eat Healthy

When Research Is Deeply Flawed. 

Here’s What You Should Know to Eat Healthy

It seems like every week, new research comes out questioning long-held wisdom about nutrition and food. First, fat was hazardous; now, it’s considered a part of a healthy diet. Eggs used to be harmful to people with heart problems due to the high amount of cholesterol, but that’s no longer the case.

Dr. David Ludwig is a nutrition professor at the Harvard School of Public Health and author of the New York Times bestseller "Always Hungry?"

This book explores the dietary drivers of hunger, obesity, and metabolic disease. In a new “Viewpoint” paper published in August in the Journal of the American Medical Association (JAMA), Ludwig and his companions explain the problems with recent dietary research approaches and why this takes to nutrition confusion.

Ludwig was asked to share advice for people who feel conflicted about how to eat.

Changing a person’s diet is much more difficult than taking a pill or a placebo, and it’s impossible to do a double-blind study with food. Diet is personal, involving deeply behavior related to family, culture, pleasure, and even values.

Changing one aspect of a diet inevitably affects many others as well. If you eat less of one food, you’ll probably eat more of another. 

In a study examining the effects of consuming 10 servings of fruits and vegetables a day, participants may naturally eat less processed foods because they’re less hungry. So it can be hard to tell whether any health benefits seen in the study are due to eating more vegetables and fruits or less of the other items. 

At the same time, food trials have difficulty determining whether and how diet actually changes. 

Apart from funding, there’s the challenging question of whether the people in these diet studies are actually following instructions.

In most trials, people are told to follow one diet or another, and they are given a very modest amount of support, maybe a meeting with a dietitian twice or thrice a month. They are then expected to adopt this major change to their lifestyle on their own. This study is especially common because of the insufficient funding and infrastructure in nutrition research. 

Inexpensive and low-intensity interventions are chosen by necessity. But you don’t really know if people follow them or ignore them.

People in diet studies don’t follow instructions.

People can make changes for a few months, but they resort back to their habitual ways of eating without enough guidelines. Because of this, we often see short-term weight loss in obesity trials, which leads to weight regain after a few months. These kinds of findings have been misinterpreted to mean the type of diet doesn’t matter. But that conclusion does not have any logic.

Imagine there’s a new drug that might cure childhood leukemia. You conduct a clinical trial with a half group of people assigned to take the new drug and another half group receiving a placebo. But it turns out the group assigned to the drug didn’t take it as instructed. In this situation, there might be no significant change in cancer treatment success. But we wouldn’t interpret that the drug is ineffective. We would conclude that the research was flawed. 

Unfortunately, the diet trials are not always held to this standard.

Many people can cut back on calories and lose weight temporarily. But after a few days or weeks, hunger increases, and their metabolism slows down, which is a clear sign for weight regain. That’s why we need longer-term studies to see how the type of food we eat might alter the success of weight-loss maintenance. 

Even the best diet in the world won’t work if people aren’t motivated to follow it. That’s why we need studies of behavior and the environment to make lifestyle changes easier and more sustainable.

Diet-related diseases — including obesity, diabetes, and heart disease — are the leading public health problems today. Whether or not you have one of these conditions, you’re paying the cost of Medicare and checkups. These costs are borne by everyone. And for people with a condition like Type 2 diabetes, the personal toll includes limb amputation, kidney failure, blindness, and shortened life expectancy. So it’s in everybody’s interest that research into nutrition and disease prevention be done properly.

Some say we can’t afford new government programs to deal with these diseases. But today, the economic cost of Type 2 diabetes approaches $500 billion annually.

The total medical costs of the diet-related disease may already exceed $1 trillion annually in the U.S. Without action, these figures will only double, contributing to the national budget deficit and threatening the international competitiveness of the U.S. economy. 

What’s lacking is a clear vision to align public health priorities with investment.

We know humans aren’t programmed to gain more weight. Something has changed around us, which is driving even highly disciplined people to gain weight. We have to understand what’s that about. 

One likely to blemish the processed carbohydrates that crept into our diet during the low-fat diet years. But that’s not the whole story; many other factors are contributing. We’ll need long-term, adequately powered research studies to sort this out once and for all.

We need to build the capacity to conduct effective nutrition and diet research, requiring sustained investment.

Advice to the general public for reading stories about nutrition research

Ideally, medical journalists need better training to identify basic flaws in clinical trials to convey a more balanced view of study strengths and limitations. We don’t want the public dragged back and forth with every weak and new research. 

As a general rule, if a clinical trial on obesity has a small number of participants (fewer than 20 people), the results can be considered weak if it’s a concise term.

More Trustworthy research journals

Some top-rated journals are the New England Journal of Medicine, the Lancet, the BMJ, Annals of Internal Medicine, and JAMA. American Journal of Clinical Nutrition also ranks at the top of the field.

Many other good-quality journals publish credible research, so a journal’s identity by itself is not the whole story.

Advice on how to Eat Healthy

I prefer a “low glycemic load” diet...…. One that controls the surge in blood and insulin after the meal. The way to achieve this is by cutting back on processed carbohydrates (refined grains, potato products, and sugar) and increasing healthy fats, like nuts and avocado, olive oil, and even dark chocolate. And include an adequate amount of protein, which can come from plant and animal-based sources.

This approach involves a reduction in total carbohydrates but still offers lots of flexibility in food choice. For people with diabetes, severe restriction of carbohydrates may have additional benefits.

Not all researchers will agree with this recommendation. That’s why we need definitive nutrition research.

Improving the quality of nutrition research will be critical to public health and America's international economic competitiveness in years to come.