Weight Regain After Dieting: Why It Happens and What Reduces It

Weight regain is the rule, not the exception, after most diet-induced weight losses. In most cases, more than half of lost weight is regained within two years, and by five years, over 80% is regained again. But some dieters, while making up a small minority, succeed in keeping weight off long-term. Looking at the mechanisms of regain and the habits of successful maintainers can guide efforts to reduce post-diet weight gain.

Biological factors set the default toward regain after weight loss, even if lost weight is modest. After most diets, resting metabolic rate remains 5-10% lower [1] than expected for the new body composition - what researchers interpreting this as the body adapting metabolism in an attempt to regain lost weight. Meanwhile, appetite-promoting hormones increase [2], while the hormones that suppress hunger decrease, making it harder to stick to the lower calorie intake needed to keep lost weight off. Together, these factors make post-diet regain more likely, and the new set point harder to defend with lowered self-restraint.

But even with the body working to regain, it does not always happen. In McGuire et al. (1999), researchers found that the dieters who had maintained weight loss for at least 5 years used more of the following habits than those who had regained weight:

-Higher levels of physical activity, especially vigorous exercise -Higher fat intake control -More frequent self-weighing

The maintainers' other eating habits were similar to those of the weight-stable control group in the study: both groups reported similar levels of diet constraint. That suggests that the success of the maintainers was not about overall restraint, but more targeted food management. It also suggests that such skills can be used to stay at an "already-thin" weight, not just to prevent regain post-diet.

More recent research finds that the same food management and activity habits continue to set successful weight-loss maintainers apart. In a 2017 study of highly successful weight loss maintainers, the most frequently-cited maintenance strategies [4] were:

• Drinking breakfast daily
• Keeping healthy foods at home
• Regular vegetable intake

These were most common "maintenance" strategies, not just "weight loss" strategies, and were reported as used daily by 85-95% of the respondents. Increasingly elaborate cuisine, gourmet ingredients, or chef skills did not correlate with great results, showing that the necessary input is probably fairly simple.

The same 2017 study adds a few more details:

• Compared to matched weight-stable controls, the maintainers showed a reduction in portion sizes and carbohydrate intake, and an increased protein intake in their maintenance phase. - Compared to matched controls, the maintainers also walked more and used weight self-monitoring more, showing the ongoing value of these skills.

The 2023 study [5] added more detail on the behaviors that set maintainers and regainers at one year apart:

• Self-monitoring was the single largest discriminator between maintainers and regainers, with a mean weight maintenance of 0.4 kg for the maintainers and a 7.2 kg gain for the regainers

• The maintainers used specific goals, reductions in portion sizes and carbohydrate intake, and increased protein intake. They exercised more while also increasing other healthy habits: more weight self-monitoring, more walking, and habitual healthy food choices.

• The regainers reduced their exercise, began eating in response to emotions, and declined their healthy habit strengths in both eating and activity. These were the major discriminators between the maintainers and regainers in the Longer-term study's data.

The 2023 study also adds some practical detail, which shows the difficulty of the regain challenge: in the gainer group, the average 1-year weight gain was 7.2 kg (16 lbs), with some gaining substantially more. Even the maintainers, the most successful group, had a modest average gain of 0.4 kg. So preventing at all takes effort, with a baseline being achieved only by a very skilled and dedicated subgroup.

A 25-year research summary of weight loss studies puts the bottom line like this: successful long-term weight maintenance is driven by eating-related self-regulation habit strength. This correlates highly with weight and habit stability. Conversely, more emotional eating, more eating in the presence of emotional triggers, and less habit strength predict relapse. The presence of a supportive environment also predicts good maintenance, while the absence of such support can likewise trigger relapse. Eating-related behavior change and maintenance is modulated by mood, highly and frequently, and mood-shifts accompany both eating relapse and success.

A long-run perspective is important, as the working models that sustain a healthy weight must integrate with the biology and habits of a long-run lifestyle. Most weight regain happens within a few years, and most regainers have not learned how to integrate their weight into their general lifestyle, at multiple months, quarters and year levels of viewing the overall process. As there is de-acquisition and loss as much as gain, the trade-offs of practices that integrate with long-term living are critical to success in the long run.

The upshot of current research: it is not only one of the easiest things that avoids regain, but is the single most powerful discriminator between regainers and maintainers. Combined with keeping healthy foods at home and eating vegetables, walking, and increasing protein a little, and reducing portion sizes a bit, these behaviors appear to be the key to maintenance. And that has been the case for over twenty years, likely making these the best bet going forward, physiologically at least.