What Is The Best Diet? Results of the DIETFITS Study

What is the Best Diet?

I know, we keep coming back to this question. I get asked this question frequently. I think that's cause lots of people are frustrated with the glut of conflicting information available, and want to know how to get results.

I wish there were a quick answer. I will say, when it comes to healthy lifestyle, I've be come obsessed with helping people understand what will produce the results they want in their own bodies. We all grow tired of the same advice of "just eat less and exercise more." While there is a certain truth to this statement, for most people such advice does not lead to changes that actually produce benefit. Something is missing.

Low-fat vs. Low-carb

Low-carb is an approach that works well for many people. Low-fat diets have fallen out of favor, although traditional low-fat diets are not the same as healthy low-fat diets that don't rely on processed foods (think vegetarian approaches that emphasize plants and whole grains).

So, how would a healthy low-carb diet compare to a healthy low-fat diet? I thought I'd share results from a study that was published in 2018 called the DIETFITS Study. The researchers in this study asked an interesting question. Specifically, if someone was more insulin resistant (think farther along on the diabetic or prediabetic spectrum), would they respond better to a particular dietary approach? One hypothesis has been that people with insulin resistance might get better results with a low carbohydrate diet.

To answer this question they recruited 609 overweight adult volunteers and randomized them to follow a healthy low-fat or a healthy low carbohydrate diet, and they monitored their responses over a full year. They also looked at 2 markers of insulin resistance, either changes in three genes known to increase insulin resistance or the blood insulin level 30 minutes after a glucose challenge, and compared the results of each dietary approach for people who were insulin resistant and for people who were not.

So, what did they find?


After one year, weight loss averaged 12-13 pounds for both groups. They did not find that people who were insulin resistant responded better to one approach than the other.

Take a look below at the key figure from that study. It shows how much weight people in various groups lost. If you are not familiar with statistical plots, what you will notice is that all of the boxes essentially line up together, which means there were no "statistically significant differences" between groups. That is, both a healthy low-fat and a healthy low-carbohydrate approach could work in people who were insulin resistant, and both approaches could work in people who were not insulin resistant.



What is the best diet? The DIETFITS study provides evidence that there is no dietary approach that works for everyone, and that there is probably more than one approach that will work for each person.

I believe the best diet is the one that helps you reach the 4 Goals for Healthy Eating. The best diet for you is the one that allows you to:

  • Achieve your weight and blood sugar targets
  • Delivers adequate nutrients
  • Allows you to enjoy eating
  • Is sustainable for you in your current life situation

Getting the results you want from your nutrition requires both (1) knowing the right approach for eating healthy and (2) following through on your good intentions and actually eating that way. It's the people who follow the program who get the results! Make sure the approach you try is likely to be sustainable for you based on your preferences and desires.


Dr. Topher Fox


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