In this study, patients with
obesity or overweight were placed on an intensive medical intervention or a conventional carbohydrate-restricted diet for 6 months; then, for up to two years, both patient groups were placed on a conventional
carbohydrate-restricted diet thereafter. Results showed that the IMI group had superior initial body weight loss at 6 months (11.9% (SD=7.4) vs. 6% (SD=6.1), p<0.001). However, by 18 months, the IMI group had regained 3.1% of their post-intervention weight, whereas the CCR group continued to lose weight. Among those who completed 2-years of follow-up, weight loss was clinically significant in both the IMI and CCR groups, but the difference between groups was not significant (7.1% (SD=10.2) vs. 8.1% (SD=6.3), p=0.735).
The reason for similar weight loss at 2-years between the treatment groups is likely due to the 18 months of carbohydrate-restricted maintenance therapy, which was the same dietary plan for both groups. Patients who were initially on the IMI treatment and subsequently placed on CCR for maintenance therapy experienced an increase in overall caloric intake during maintenance therapy. This may be the cause of the greater weight regain in the IMI group, relative to the CCR group. Nonetheless, although the differences between the IMI and CCR groups were greatest initially and decreased over time, the differences between groups averaged across 2 years were substantial, with an adjusted 2.8% (95% CI=(1.7%,3.9%), p<0.0001) greater BWL among the IMI group.
In comparison to results from published trials on carbohydrate-restricted diets, the IMI treatment group demonstrated nearly twice the documented weight loss at 6 months (11.9% BWL (SD=7.4) vs. 6% BWL (SD=6.1), p<0.0001). As expected, the CCR arm demonstrated equivalent weight loss to similar carbohydrate-restricted dietary programs from other institutions [
9,
10].
When the results of our study are compared to commercially available nonmedical weight loss programs, both the IMI and CCR groups demonstrated superior weight loss results [
11]. Based on the results of randomized controlled trials, participants who use nonmedical commercial weight loss programs, such as Weight Watchers and Jenny Craig, lose approximately 5% of their initial weight over 3 to 6 months, and maintain 3% BWL at 2 years [
12-
14]. It is important to note, however, that weight loss of this magnitude is not trivial and can be associated with reductions in obesity-related comorbidity and mortality [
15].
Very low calorie diets (VLCD) provide a meaningful comparison to our study’s IMI due to similarities in program structure. VLCDs involve a complete replacement of regular meals with food or formulations that provide 400-800 calories daily, which are typically used under medical supervision, and induce rapid weight loss [
6]. In a study of 40 obese patients on VLCD of 800 kcal/day, participants who had meal replacements and one conventional meal per day lost 14.1% of their initial weight at 3 months and 8.4% at one year [
16]. Another multicenter study evaluated 517 individuals who entered a commercially available 26-week VLCD program. Patients who completed treatment lost 21.8% of their initial weight. Of the 43% of patients who had 1-year follow-up, mean BWL was 9.0% [
17].
Based on these data, some investigators argue in favor of VLCD, noting that it induces excellent initial weight loss [
18]. However, weight regain is significant, with approximately 8-9% BWL at 1 year, and only 5% at 4 years [
11,
19]. The IMI utilized in our study induced less initial weight loss at 6 months relative to a VLCD, but superior weight loss at one year and beyond, presumably due to increased dietary compliance with the carbohydrate-restricted maintenance therapy.
It has been suggested that rapid weight loss, when achieved in conjunction with an appropriate long-term weight management program, is successful in maintaining clinically significant weight loss over time [
20]. Yet, because weight regain is a common cause of long-term failure among successfully treated patients with obesity or overweight, the choice of maintenance therapy is paramount. In this study, the choice of a carbohydrate-restricted diet as maintenance therapy was based on multiple large randomized trials demonstrating that diets moderately high in protein content improved the likelihood of weight loss maintenance [
21-
24]. The underlying physiology of weight loss due to carbohydrate restriction with increased protein consumption involves rebalancing the insulin-glucagon ratio in favor of lipolysis [
1,
6], but the long-term effectiveness of carbohydrate-restricted maintenance therapy is likely multidimensional-involving changes in thermogenesis, satiation, and sustainability, rather than a dietary shift in macronutrient composition alone.
Overall, our study demonstrated significant weight reduction at 24 months regardless of the treatment arm (IMI: 7.1%, CCR: 8.1%). However, based on our results, males and those with higher BMI achieve more weight loss under the IMI plan. Bischoff et al. also found that males fared better with their
low calorie diet intervention, and speculated that males may have done better because they initially had higher BMI, and also because daily calorie restriction means more pronounced restriction for males than females [
7]. Being that males have high rates of success; such intensive medical interventions may be considered as an alternative to surgical weight loss for males with higher BMI. Additionally, the IMI may be considered as a safe and effective choice for preoperative weight loss prior to bariatric surgery, or other interventions that benefit from preoperative excess weight loss, such as transplant and orthopedic surgery. The IMI may also be beneficial among patients who are resistant to induction of weight loss or unable to tolerate weight loss medications.
The significance of factors predictive of weight loss success in the CCR group, namely higher initial SBP and TSH, is less evident. An interpretation may be that patients with increased medical comorbidity may have greater motivation to lose weight and therefore succeed with a conventional carbohydrate-restricted diet.
Strengths of this study include the duration, sample size, and assessment of a novel weight management program. All body measurements were obtained by trained professionals and not through patient self-reporting. The study assessed both primary weight loss and maintenance of weight loss.
Limitations include the single center nature of the study. Patients were not prospectively randomized to treatment arms and therefore the study may be subject to more biases and confounding than a randomized controlled trial; on the other hand, it has been speculated that adherence and clinical outcomes improve when participants are able to freely select their weight-loss program, and thus randomization may underestimate the true effect of medical weight management programs [
9,
25,
26].
Attrition rates were also significant, although the attrition rates reported in this study are similar to many other published medical weight loss studies [
7,
9,
27], highlighting dropout and attrition as an area of much needed improvement in medical weight management. Lastly, we did not analyze our data by using a baseline-carried forward analysis because this would artificially inflate the power of our long-term data and dampen the true effect of our intervention. Certainly, a future assessment of the IMI should include randomization, improved long-term follow-up, and a full assessment of amelioration of co-morbidities with thorough laboratory assessment.
In 2013, the American Medical Association changed its classification of obesity from “a major public health problem” to a disease. One of the objectives of this change was to encourage third-party payers to increase coverage for obesity treatment. Presently, reimbursement for medical management of obesity is minimal, whereas coverage for bariatric surgery is increasing. Hopefully, as medical management continues to evolve with improved weight loss and maintenance outcomes, increases in reimbursement for medical management will follow suit.
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