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The psychology of weight loss.

The Perfect Diet Does Not Exist

Why we need to end the diet debates

My colleague, Dr. Brad Appelhans and I wrote an editorial that came out today in the Journal of the American Medical Association entitled, A Call for the End to the Diet Debates.  When I say “diet debates” I’m referring to all the bickering about which diet is the best for weight loss. Is it low-carb?  low-fat?  Mediterranean?  Paleo?  The answer is:  it doesn’t matter.

In the past year, 5 meta-analyses have been published summarizing studies of diets that vary based on their carbohydrate, fat, and protein content.  (A meta-analysis is a study that compiles the findings from a bunch of studies in order to evaluate the overall effect of the diets across trials).  The 5 meta-analyses included 13, 15, 20, 23, and 24 studies, respectively.  That’s a lot of research!  Here are the results:

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Summary of Meta-Analyses on Diet Comparison Studies*

1. Bueno et al 2013

Low carb ketogenic diet  vs Low-fat diet

13 studies

Weight loss difference:    2 lbs (low carb)

2. Wycherley et al 2012

High protein/low fat  vs  Standard protein/low-fat

24 studies

Weight loss difference:     1.7 lbs (high protein/lowfat)

3. Hu et al  2012

Low-carb vs Low-fat

23 studies

Weight loss difference:  NONE

4.  Ajala et al  2013

Low-carb, Vegetarian, Vegan, Low-GI, Mediterranean, High-protein vs Low-Fat

20 studies

Weight loss difference:   Low-carb > low fat by 1.5 lbs.

Mediterranean > low-fat by  4 lbs

All other diets no different from low-fat

5.  Schwingshackl et al 2013

High-protein vs Low-Protein

15 studies

Weight Loss Difference:    NONE.

The bottom line?  No single diet consistently comes out as better than the others. Sometimes low-carb outdoes low-fat, sometimes it’s a draw.  The biggest difference was that the Mediterranean diet outdid low-fat but only by 4 pounds.  Most people wouldn’t mind losing an extra 4 pounds, however, I would not base your pick on the 4 pounds but rather on how much you dig the Mediterranean diet because at the end of the day it is the diet you can stick to that will be the perfect diet for you.

The common finding in research is that how long one sticks to a diet is associated with how much weight is lost and how long that weight stays off.  Picking a diet should be like picking a spouse-- not a one night stand.  If you plan to be on your diet temporarily, your weight loss will be temporary.  Which diet do you want to marry til death do you part?  That question is up to YOU not researchers or diet gurus trying to sell books.

Do we need more research comparing diets?  You decide.  Some researchers would point out that there are variations we still haven’t tested or methodological details that still need tweaking.  My opinion is more research comparing diets differing in carb/pro/fat is unlikely to significantly advance the field of obesity management.

It's not WHAT you are eating, it's HOW to make healthy habits stick.  My patients often tell me they are having trouble losing weight not because they don’t know WHAT to eat, but because they can’t figure out HOW to get those new healthy habits to stick.  This is the question researchers should be focusing on! How do we make long-term behavior changes?  We need to develop better strategies to help us navigate this unhealthy environment of ours.  We live in a society where you can get a bacon double cheeseburger in 5 minutes almost no matter where you live. We need to equip ourselves with a defense against the ubiquity of unhealthy foods that our brains are wired to strongly desire.

Why do we make unhealthy choices when we say we want to live a healthy lifestyle?  Our ability to live a healthy lifestyle is often thwarted by immediate pleasures in the environment, stress, and a host of other factors that we are only beginning to understand.  Nobody is immune to making the occasional unhealthy choice yet when someone succumbs we lay blame.  Because we don’t fully understand why people make decisions that conflict with their overarching desires, we conclude that they must not be motivated or that they are just plain irresponsible.  Such explanations of behavior are likely bore out of the frustration of not knowing, they lack insight and prevent the inquiry that is needed to obtain a richer knowledge of human behavior.

"Diet" mentality may be more harmful than helpful   Asking people to adhere to a diet with strict rules about carbohydrates, protein, and fat may be more harmful than helpful.  Diet isn't a one-size-fits-all and it will never be.  Helping people design an approach to eating that fits their personal preferences has a better chance of long-term success.  Behavioral modification strategies that help them navigate the bumpy road are essential.  My hope is that we invest in research that further identifies behavioral strategies that help us navigate this unhealthy environment as well as research that identifies environmental changes that can set us up for success.

For help with weight loss, see the Table of Contents of this blog to see a wide range of posts on behavioral challenges to weight loss. 

Footnote:

*It may be the case that some of these reviews included some of the same studies but even if they were entirely overlapping (which they are not) we’d still have at minimum 24 studies comparing diets and as many as 95.

References

Pagoto, SL & Appelhans, B.  A Call for the End to the Diet Wars.  Journal of the American Medical Association, 2013, 310:7; 687-688.

Ajala O, English P, Pinkney J. Systematic review and meta-analysis of different dietary approaches to the management of type 2 diabetes. Am J Clin Nutr 2013;97:505-16.

Wycherley TP, Moran LJ, Clifton PM, Noakes M, Brinkworth GD. Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials. Am J Clin Nutr 2012;96:1281-98.

Hu T, Mills KT, Yao L, et al. Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors: a meta-analysis of randomized controlled clinical trials. Am J Epidemiol 2012;176 Suppl 7:S44-54.

Bueno N, de Melo I, de Oliveira S, da Rocha Ataide T. Very low carbohydrate ketogenic diet v low-fat diet for long-term weight loss: A meta-analysis of randomised controlled trials. Br J Nutr 2013;epub ahead of print.

Schwingshackl, L, Hoffman, G.  Long-term effects of low-fat diets either low or high in protein on cardiovascular and metabolic risk factors:  A systematic review and meta-analysis.  Nutrition Journal 2013, 12: 48.

Sherry Pagoto, Ph.D., is an Associate Professor of Medicine, Division of Preventive and Behavioral Medicine, Department of Medicine at the University of Massachusetts Medical School.

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