• Dr. Dawn Harris Sherling

Which diet is best for losing weight?



Which diet is best for losing weight?


That’s a question I’m asked a lot. And it’s a good one. Given our current obesity epidemic, it might rank up there in importance with the age-old question, “What is the purpose of life?”


Few seem to have a straight answer for that one, except for people who have deeply held religious or ideological beliefs. And so it is for diet too. Keto adherents are quite sure that avoiding carbs is the way to go. For vegans, avoiding animal products provides the clear path to health. If you’d like to experience the passion of a religious war without the bloodshed, head over to Twitter and read a few keto responses to a vegan post or vegan responses to keto posts. While they may not actually be killing each other, each is convinced that the other’s dietary habits will do it for them.


Enter Kevin Hall, Ph.D., at the National Institutes of Health (NIH) who decided to play peacemaker with a healthy dose of science. Dr. Hall designed a study where participants would be fed either a high-fat, low carb diet (like keto) or a low-fat, high carb diet (like a whole-food, plant-based diet)(1). The participants had two weeks in each arm of the trial, so were basically being compared to themselves. Like a previous study he had done at the NIH looking at an ultra-processed diet vs. a whole foods diet, all the food was provided to the participants and their activity was carefully tracked. Also like that study, participants could eat as much as they wanted and the food was pretty good.


The folks on the low-fat diet ate about 500-700 fewer calories a day and had higher insulin and blood sugar levels. The people doing the high-fat diet ate more calories but had lower insulin and blood sugar levels (as might be expected). So, which diet caused more weight loss?


The short answer is that they both resulted in weight loss, but the low-fat diet resulted in more body fat loss in the participants. Case closed. The vegans win, right? But wait! These weren’t restrictive diets. I told you earlier that the people in the study could eat as much as they wanted. Neither the low-fat nor the low-carb participants were hungry and they both lost weight. How?


Here’s where we need to go back to Dr. Hall’s previous work on ultra-processed vs. whole foods diets (2). Participants in this prior study lost about 2 pounds on the whole foods diet and gained 2 pounds on the ultra-processed one. When he designed the low-fat vs. low-carb study, he pretty much avoided giving the participants ultra-processed foods (examples here: https://www.nih.gov/news-events/nih-research-matters/low-fat-diet-compared-low-carb-diet).


OK, but the vegans still win, right? Sort of. Plant-based diets are probably better for you, both in the short term, like in this study and in the long term, as Dean Ornish and others have shown with improved cardiovascular outcomes. So, if you can avoid eating animals, that might be best for you and the environment. But even if you can’t (and I can’t either so don’t feel bad), if you can avoid ultra-processed foods (think stuff that has ingredients on the list that you wouldn’t have in your own pantry or in anyone’s pantry for that matter), you’ll be a lot healthier and quite possibly weigh a bit less too. (You can also check out my ingredients to avoid list here—designed for IBS sufferers but probably a good place for all of us to start): https://www.dawnharrissherling.com/post/glossary-of-additives-to-avoid-and-why


So, how do I answer the question, “Which diet is best?”


It turns out that it’s not so complicated after all: Any that avoids ultra-processed foods that you can stick with.



1. Hall KD, Guo J, Courville AB, Boring J, Brychta R, Chen KY, Darcey V, Forde CG, Gharib AM, Gallagher I, Howard R, Joseph PV, Milley L, Ouwerkerk R, Raisinger K, Rozga I, Schick A, Stagliano M, Torres S, Walter M, Walter P, Yang S, Chung ST. Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nat Med. 2021 Feb;27(2):344-353. doi: 10.1038/s41591-020-01209-1. Epub 2021 Jan 21. PMID: 33479499.


2. Hall KD, Ayuketah A, Brychta R, Cai H, Cassimatis T, Chen KY, Chung ST, Costa E, Courville A, Darcey V, Fletcher LA, Forde CG, Gharib AM, Guo J, Howard R, Joseph PV, McGehee S, Ouwerkerk R, Raisinger K, Rozga I, Stagliano M, Walter M, Walter PJ, Yang S, Zhou M. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metab. 2019 Jul 2;30(1):67-77.e3. doi: 10.1016/j.cmet.2019.05.008. Epub 2019 May 16. Erratum in: Cell Metab. 2019 Jul 2;30(1):226. Erratum in: Cell Metab. 2020 Oct 6;32(4):690. PMID: 31105044; PMCID: PMC7946062.


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