Slow and Steady May Not Win the Race for Weight Loss Maintenance

Commentary

The failure of most diets to produce durable weight loss is a frustration for patients, clinicians, and researchers. In general, regardless of the composition of a diet, the majority of patients will regain some or all of their lost weight within several years after completing the diet. The reasons for weight regain are complex, and include reversion to old eating or physical activity behaviors but also a strong physiologic drive by the body to reverse weight loss that it perceives as a threat to health [1].

One area in diet research that has recently generated some controversy is whether or not rate of initial weight loss might impact a patient’s ability to maintain that weight loss, with the conventional wisdom (and national guidelines, in some cases), suggesting that slower weight loss is preferable to rapid weight loss for this reason [2]. A handful of studies have challenged this notion, however, and suggested that rapid weight loss does not necessarily lead to greater weight regain [3,4]. Previous such studies, however, have not generally been designed to compare regain after equal amounts of weight loss, which may make their results more difficult to interpret.

The present study contributes another piece of evidence to the argument that rapid initial weight loss may not increase a patient’s risk of regain. This small randomized trial is timely and has several features that make it a unique contribution. First, the design of the study allowed for both groups, despite losing weight at very different rates, to reach the same amount of total weight loss before being followed forward in time. This made weight regain much easier to compare between groups during follow-up. Second, the study included measurement of changing body composition—ie, what kind of weight was being lost (fat vs. fat-free mass)—rather than just the total amount of weight. This allowed the researchers to present data for an outcome that is mechanistically related to metabolic rate (and therefore weight regain), and one that might have implications for longer-term health after rapid versus more moderate-pace weight loss.

Several aspects of the study design, however, may limit the impact of the findings. For example, in both arms, while a certain type of diet was “prescribed,” there is no comment about assessment of participant fidelity to the prescribed diet, and there is potential for very different levels of adherence between groups, especially in active weight loss, when basically all meals were provided to the VLCD arm, but LCD subjects were responsible for about 90% of their own meals. This could have led to larger discrepancies between prescribed and actual diet in the LCD arm relative to VLCD. Granted, the rate of weight loss was the exposure of interest, and that clearly varied between groups as expected, implying at least moderate fidelity to prescribed caloric content of each diet, but how much protein vs. fat vs. carb was actually consumed by each group is not clear. Additionally, while 9 months of post weight-loss follow-up is certainly a good start in terms of follow-up duration, it may not have been sufficient to observe differences that would later emerge between the groups for weight regain. Other long-term weight loss maintenance studies have followed patients for several years or longer after initial weight loss [5].

Using data from all participants, the researchers reported that the amount of FFM an individual lost was a predictor of weight regain during follow-up. This finding is in keeping with the idea that more lean mass loss leads to lower metabolic rate and predisposes to weight regain (hence the conventional wisdom to avoid rapid weight loss with low-protein diets). In keeping with this theme, VLCD patients, whose protein intakes and activity levels were lower, did lose more FFM (ie, lean mass) than LCD patients. It was therefore surprising that in between-group analyses there was no statistical difference in weight regain. On some level, this raises concerns about the robustness of the overall finding. Perhaps with a larger sample, more precise measures of FFM lost (eg, with DEXA scanning instead of the “bod pod” or longer follow-up, this difference in lost lean mass between groups actually would have predicted greater weight regain for VLCD patients. The researchers attribute some of the FFM loss after the caloric restriction phase to decreased water and glycogen stores, rather than muscle mass, and speculate that this is why no impact on weight regain was seen between groups.

From a generalizability standpoint, there are important safety concerns with the use of VLCDs, aside from subsequent risk of weight regain, that are not addressed with this study. Many patients simply cannot tolerate a 500 kcal per day diet, including those with more severe obesity (who have higher daily energy requirements) or those with complicated chronic medical conditions who might be at higher risk of complications from such low energy intake. Accordingly, these kinds of patients were not included in this study, so it is not clear whether results might generalize to them.

Applications for Clinical Practice

Despite the conventional wisdom that slower weight loss may be more sustainable over time, several recent trials have suggested otherwise. Nonetheless, rapid weight loss produced with the use of VLCDs is not appropriate for every patient and must be carefully overseen by a weight management professional. Furthermore, rapid weight loss may place patients at increased risk of preferentially losing lean mass, which does correlate with risk of weight regain and could set them up for other health problems in the long-term. More studies are needed in this area before a definitive judgment can be made regarding the long term risks and benefits of rapid versus moderate-pace weight loss.

—Kristina Lewis, MD, MPH