The Science on Dieting and Weight Loss

Dieting and “lifestyle programs” can feel so seductive in a culture that tells you your body is wrong and needs to be fixed. But what does the science actually say about dieting for weight loss? Does it work? Is it sustainable? Does it improve our overall health? We’re diving into all of that and more in today’s post.Content warning: mentions of stigmatizing language around weight used in research, weight loss numbers

New Year, New Me messaging is rampant at the beginning of the year and with that comes an onslaught of new year’s resolutions and diet companies’ marketing in full force.

I’ve heard January referred to as “National Dieting Month” because so many diet / wellness / “lifestyle” companies (or whatever they are calling themselves these days) are pervasive this time of year, and many people are especially vulnerable to their marketing messages entering a new year.

What the $77B diet industry is not telling you is all of the research that shows diets don’t work in the long term. Because their bottom line relies on repeat customers – the same folks trying their program again, and again, and again.

It’s helpful to know what the scientific literature says about dieting and weight loss but even more important (IMO) than research is YOUR lived experience. Have diets worked for you in the past? How long did they work for? Did you end up eventually gaining the weight back? Have diets / lifestyle programs felt sustainable for you? Why or why not? You know your body best.

The research on dieting and weight loss

A 2007 review of the scientific literature on dieting and weight loss by Mann et al. found that only 14 research studies looked at weight loss outcomes 4 years or more out. Meaning that all the other literature on diets and weight loss have very short-term follow-up (typically 1 year). These study designs benefit the diet industry because we know that diets work in the short-term but anywhere from a couple to several years out most people gain the weight back.

The review found that of the studies they looked at, participants lost anywhere between 10-65 lbs. At follow-up, most of the weight had been regained. Results ranged from a net 15lb loss to a 8lb weight gain from where they started.

30-64% of participants ended up at or above the weight where they started before the diet.

Only 9% of participants ended up with a BMI less than 35. And those who lost greater than 15% of their weight actually doubled their risk of mortality.

A 2018 umbrella review of meta-analyses on weight loss interventions found that there is “no high-quality evidence to recommend treating ‘obesity’ with a specific nonsurgical or non-pharmacological intervention among many available.” AKA we have no good evidence to recommend diet or lifestyle interventions for weight loss.

Naturalistic studies (where you observe folks in their natural environments and record behaviors) have concluded that dieting is actually a predictor for weight gain. So not only do diets not work but they also predict weight gain. Some meta-analyses and comprehensive reviews have reported the same outcomes – that lifestyle interventions actually lead to weight gain, especially with long-term follow-up.

Other reviews have shown that 3-5% weight loss is possible for years later if all aspects of treatment are maintained. To give that more context, that would be a weight loss of 6-10 lbs for a 200 lb person. Health benefits of this kind of modest weight loss are not clear. And most people are looking for a 30% weight loss, not 3-5%. 

Are health risks associated with weight due to weight cycling?

Studies show that weight cycling (losing weight, gaining it back, rinse and repeat) is a risk factor for diabetes, dyslipidemia, poorer self-perception, insulin resistance, hypertension, and visceral fat.

A 15 year study showed that the highest mortality rate was in people who lost weight and not in those who gained weight or stayed weight stable. This and other studies shows us that weight cycling may be worse for your health than staying at / maintaining a higher weight.

What if the health risks we see associated with weight are actually due to the repeated attempts to lose weight and the stress that puts on the body and not the actual size of the body?

We know that health-promoting behaviors (exercising, eating more fruits and vegetables, getting enough sleep) can reduce mortality risk regardless of any weight changes. Yes, that’s right. You can improve your health markers without losing any weight.

It’s also important to consider how weight stigma or anti-fat bias plays a role in the correlational data we see between higher weights and poorer health outcomes. It’s been stated in the literature that “bias may impair efforts to engage in healthy lifestyle behaviors through negative emotional distress and unhealthy eating patterns.”

It also feels worth noting that all studies on weight and health risks are correlational. And when you learn how to read and analyze research, the one thing that always gets stressed is “correlation does not equal causation.” We cannot say that weight causes chronic disease – there’s no literature that supports that.

If you look at all the data on smoking / tobacco use and lung cancer and see that there is a correlation between those with yellow stained teeth and lung cancer, you would never say that yellow teeth caused the cancer, you would say that’s a side effect of smoking. Yellow teeth is not a behavior. 

Just because weight is correlated with chronic disease doesn’t mean it is the cause. Weight is also not a behavior. 

“Overweight” BMIs have the lowest risk of mortality

We have been sold the belief that being “overweight” is bad for your health. What we have not heard is that studies show being “overweight” has a lower risk of mortality compared to “normal weight.” A BMI of 30-34.9, referred to in the medical field as “class 1 obesity” has also been shown to not have a higher risk of mortality compared to “normal” weight.

Why is no one talking about the protective effect of being “overweight?” Because that wouldn’t bode well for all the pharmaceutical companies selling weight loss medications and the diet industry selling their lifestyle programs. 

BMI is complete bullshit anyway but I could write another whole blog post on that topic so I’ll save it for another time.

References:

Lissner, L., Odell, P. M., D’Agostino, R. B., Stokes, J., Kreger, B. E., Belanger, A. J., & Brownell, K. D. (1991). Variability of Body Weight and Health Outcomes in the Framingham Population. New England Journal of Medicine, 324(26), 1839–1844. https://doi.org/10.1056/NEJM199106273242602

Tolvanen, L., Ghilotti, F., Adami, H.-O., Ye, W., Bonn, S. E., Bellocco, R., & Lagerros, Y. T. (2023). Prospective study of weight loss and all-cause-, cardiovascular-, and cancer mortality. Scientific Reports, 13(1), 5669. https://doi.org/10.1038/s41598-023-32977-8

Mulligan, A. A., Lentjes, M. A. H., Luben, R. N., Wareham, N. J., & Khaw, K. T. (2018). Weight change and 15 year mortality: results from the European Prospective Investigation into Cancer in Norfolk (EPIC-Norfolk) cohort study. European journal of epidemiology, 33(1), 37–53. https://doi.org/10.1007/s10654-017-0343-y