In one of its main areas of inquiry, nutrition science is stuck in a rut. Weight loss research has become Einstein’s definition of insanity; repeat the same thing over and over and expect different results each time.

Diet A vs. Diet B. Low-carb vs. low-fat. Control protein. 5-7% target bodyweight loss to be “significant”. And one thing we know: it doesn’t matter. Diet A, B, C, D, or Y and Z: they all work. Except they don’t. Results are published as “significant” despite the fact that the true significance in what we have learnt from weight loss research is the paucity of evidence for long-term maintenance. We’re all familiar with the statistics by now: up to 35% of weight lost in an intervention will be regained after 1-year, and by 5-years practically all – or a majority – of weight lost will have been regained [1].

Which brings us to the subject of this article: is there any evidence for long-term maintenance of weight loss? What is the difference in the types of intervention that are successful in achieving long-term maintenance? What are the characteristics of successful participants? And is there anything we can glean from this limited data set to inform where investigations might look further?

This article will attempt to examine these questions.

 

Evidence for Long-term Weight Loss Success

Evidence for long-term maintenance is not absent the literature, but it is scarce. Two factors which should be considered is the definition of ‘successful weight loss’, and definition of ‘long-term’. The framing of these two factors may often lead to a misleading interpretation of the data. ‘Success’ is typically defined as a 5-10% loss of initial bodyweight; these targets are not necessarily arbitrary, and are established by reference to clinically significant reductions in risk factors for type-2 diabetes and heart disease that are also considered achievable for the individual [this latter premise will be discussed further below]. [2][3][4][5]

‘Long-term success’ is often defined as maintenance of lost weight for 1-year [6]. This is potentially misleading for two reasons. The first is the misrepresentation of the time-course of weight regain, given that weight regain over 1-year is highly predictive of continuing weight regain beyond that timepoint [7]. Using 1-year as a time-point thus misrepresents the definition of ‘successful’ weight maintainers. The second, and more important factor for our purposes, is that the crucial period for maintaining weight loss over the long-term also appears to be the period going beyond 2 years and up to 4-5 years [8][9][10]. In analysis comparing participants in a weight loss trial whom maintained weight loss beyond 1-year against participants who regained weight, the single greatest predictor of weight regain was duration of weight maintenance: successfully maintaining weight lost beyond 2-years exponentially increased the likelihood of success, with a 50% reduction in risk for weight regain between 2-years and 4-years [8]. Maintenance over 5-years reduced risk of regain by 71% [8]. The picture that emerges is that duration of time spent in maintenance is a critical factor. Where weight has already started to be regained within a 1 to 2-year period, the odds of weight regain continuing in an almost linear fashion are significant [7][8].

This trend toward almost immediate weight regain must also be considered in the context of absolute weight lost. Indeed, one of the observations from diabetes literature is that there may be a legacy benefit to weight loss, even if a significant proportion of initial weight loss is regained [11]. In the Look AHEAD trial, a diabetes prevention lifestyle intervention program, mean weight loss in the intensive intervention group was 8.5% bodyweight after 1 year, and 4.7% at year 4 [9]. However, by year 8 of the program there had been a stabilising effect on weight in the intensive intervention group, with mean weight loss remaining on average 4-4.7% between years 4 and 8 [10]. Scrutinising the means closer, it emerged that subjects whom lost >10% of bodyweight during the initial 1-year intervention were significantly more likely to maintain between 5-10% weight loss at 4-years: 42% had maintained 10% of weight loss [a staggering number relative to the wider literature], while 70% had maintained >5% loss [9][10]. At year 8 of the intervention, those numbers remained 39% and 65%, respectively, rendering this trial the single most successful long-term intervention of its kind [10].

Two observations emerge from scrutinizing the evidence for long-term weight loss maintenance. The first is that the period between 2 and 5-years post weight loss appears to be critical, with duration of maintenance a key determining factor increasing the odds of maintaining significantly beyond two years and linearly improving up to and beyond 5-years [7][8][9][10]. In this context, 5-years is a more appropriate time point to consider weight loss maintenance ‘successful’. The second is that we need to consider both the absolute level of initial weight loss and weight regain, within the context of these timeframes. One possibility is that greater initial weight loss may increase the likelihood of successful maintenance over the long-term; the other is that greater initial weight loss may mean that a certain degree of weight regain still results in a net benefit over the long-term [9][10].

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