Christopher Gardner, PhD, talks about his research on popular weight-loss diets, the four fundamental principles of healthy eating, and how health care professionals can help patients find an eating pattern that works for them.

Q: What are the biggest challenges to understanding the way Americans think about diets?

A: “Diet” is a really fascinating word for me. As a nutrition professional, I think of the Mediterranean diet, the Asian diet, a weight-gain diet, a weight-loss diet, and so on. But the American public thinks of a diet as something you’re going to go on, which is the worst possible way to think of it. If you’re going on something, that almost definitively means you’re going to go off it when you’re done.

People tend to go off diets for two reasons. First, they try it, it doesn’t work, and they give up. Second, they go on an extreme diet until they achieve a certain weight-loss goal, and then they go off the diet and everything goes back to the way it was before.

If a diet is something that you go on and off, it’s not going to help you. Instead you should have an eating pattern, not necessarily a diet, that you enjoy and can see doing for the rest of your life, and you can keep modifying and improving it.

Q: Can you talk about your research on popular diets?

A: I’ve done a number of weight-loss studies, including the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) study, that we finished recently. I never intended to study weight-loss diets. When I got a PhD in nutrition science, I was interested in studying the health benefits of phytochemicals. I once gave an hour-long talk on the phytochemicals in garlic, but the audience only asked questions about whether the Zone or Atkins diet was better. And so, I wrote a grant and did a study comparing popular weight-loss diets.

As I reviewed the literature on diets, I was frustrated to see that some studies were biased. For example, a study comparing low-carb and low-fat diets might make the low-carb diet more interesting and rigorous, with no added sugar but plenty of fiber, and just give the low-fat group a booklet and allow them to eat refined grains and added sugar. Refined grains and added sugar are low-fat, but that’s a low-quality, low-fat diet.

In my diet studies, we tried to get rid of any bias by designing the best versions of these diets to put them on equal ground. For the DIETFITS study, which compared low-carb and low-fat diets, both diets shared four fundamental principles:

• as many vegetables as possible, especially non-starchy ones
• whole foods as much as possible
• little or no refined sugar
• little or no refined grain

The study looked at whether a genetic marker or a metabolic marker would predict who would do better on a low-fat or low-carb diet, but both of those markers failed to differentiate success. Both groups were successful in losing weight, but there was an enormous amount of individual variability. Within each group, somebody lost 60 pounds, and somebody gained 20 pounds, and the rest of the participants were on a continuum in between. I believe we had the wrong markers, not that personalization is impossible. The results led me to believe that those four fundamental principles work for everybody, and there’s still room for personalization.

Anecdotally, some people seemed to feel more satiated on a low-carb diet, others on a low-fat diet. And for some people, certain foods are more pleasurable than others. Over time, nutrition professionals have gotten so hung up on health issues that we’ve lost the idea of joy and pleasure in food. If we tell somebody to change the foods and beverages they’re consuming, and they don’t like it or they’re hungry, they won’t stick to it.

Q: What research is being done to help us better understand dieting and diabetes?

A: Some studies using continuous glucose monitors (CGMs) have shown that different people eating the same exact food have different blood glucose responses, and the same person eating the same food in different contexts has different blood glucose responses.

We’re starting to do some studies with CGMs, and study participants are fascinated when looking at the blood glucose spikes that occur in response to foods and how spikes go down and get blunted when they experiment with portion size, timing, and what else they eat. CGMs allow people to personalize what they eat to have a more stable blood glucose level.

Another hot topic of research is intermittent fasting. However, it’s going to be difficult to answer questions about intermittent fasting because there are so many different ways to intermittently fast: no food every other day, eating half the calories every other day, eating only between certain hours, and so on. Another problem is ensuring and assessing participant adherence. It’s going to take a long time to have evidence about intermittent fasting. And even if intermittent fasting does work, different patterns probably work for different people.

Q: How can health care professionals educate patients about nutrition, dieting, and the risks of fad or extreme diets?

A: Health care professionals should dissuade patients from trying fad diets and extreme diets. Fad diets, by their very definition, don’t last. Researchers can’t get funding to study a fad diet. Studies require years to recruit and follow participants; by the time the study is finished, a fad diet would be out of fashion. Proponents of a fad diet can say that there’s no evidence against it, but I would say, there’s no evidence for it.

Extreme diets are the hardest to keep up. For the DIETFITS study, we did a sub-analysis of the 5 to 10 percent of participants who achieved the best adherence—the lowest carb diets or lowest fat diets—in the first 3 months of the study. At 12 months, there were very few metabolic or weight differences between the most adherent low-carb and low-fat groups; both groups did fabulously well. However, there was massive recidivism among those extreme adherents; they couldn’t keep it up.

Health care professionals should also walk their own talk and spend more time on food and cooking. Data show that when doctors exercise more, cook more, and eat better and tell their patients to try it, their patients are much more likely to do it.

Q: How should health care professionals talk with patients who have diabetes about diets and healthy eating patterns?

A: Health care professionals can find advice for working with patients with diabetes in Nutrition Therapy for Adults With Diabetes or Prediabetes: A Consensus Report. For that report, we worked really hard to look at all the new evidence on nutrition for people with diabetes and prediabetes. We don’t have perfect evidence, but we came together as a group of research experts to evaluate the evidence that we do have and come to a consensus. These are the statements that you could and should feel comfortable using with your patients. In the report, bullets and shaded boxes highlight the major takeaways.

As I mentioned, studies using CGMs have shown that different people have different blood glucose responses to foods, and people have different blood glucose responses to the same food in different contexts. If CGMs become more accessible, in theory, people could wear a CGM for a time to learn more about their metabolism and personalize their own strategy. But until CGMs are more common, health care professionals can convey that different people have different blood glucose responses to foods and beverages, which has to do with timing, portion size, and what you eat and drink before and after.

How do you address popular diets and weight loss with your patients who have diabetes? Tell us below in the comments.