Monday, December 4, 2023
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A number of lifestyle, medication, and surgical resources are now available that produce meaningful weight loss and maintain that loss for some time.[90] However, the body's drive to regain is strong and few resources are able to succeed for the long term. Weight regain remains problematic regardless of the weight loss method.[91] It may be that the weight-management paradigm requires different short- and long-term strategies to be applied in order to override the 3 potential drivers of weight regain: biology, behavior, and the environment.
Rat studies indicate that both a high-fat diet and little activity will lead to weight gain, and the inverse is true for weight loss. To maintain weight loss, the diet and exercise controls must remain, but if the rats are allowed to, they will revert to the original food and activity levels and weight. To explain the metabolic adaptations to weight reduction that promote weight regain, the proposed model involves changes in both fuel storage and utilization. Also, while metabolic factors favor weight regain, daily exercise decreases the rate of weight regain at all time points.
Leibel[92] found weight loss to be associated with lower energy expenditure post weight loss, and Astrup[93] reported a lower resting metabolic rate (RMR; -2.9%) in formerly obese subjects compared with normal-weight controls (adjusted for fat and fat-free mass). Also, more obese individuals had a lower than expected adjusted RMR vs controls (prevalence 15% vs 4%) and fewer had a higher than expected RMR (8% vs 12%). These data were contradicted by the National Weight Control Registry (NWCR), a cohort comprising approximately 6000 "successful losers" who have lost 30 lb or more and maintained this loss for at least 1 year. The NWCR found that in 85% of reduced-obese individuals there was no permanent obligatory RMR reduction beyond that which was expected for lean mass loss.[94]
In reduced-obese adults, a number of studies have suggested a reduced capacity for fat utilization,[94-96] suggesting that the fat oxidation differences may be one biological factor driving weight regain. The respiratory exchange ratio is a measure of fat and carbohydrate utilization, with a lower value indicating greater fat oxidation. Although these studies found low fat-oxidation rates, it is difficult to know whether this is due to the dieter's selection of a low-fat diet.[97]
Other aspects of energy expenditure that contribute to the biological drive for weight gain include: (1) improved work efficiency in skeletal muscle after weight loss, meaning that less energy is expended per any given work load[79]; (2) in nonobese adults, resistance to fat gain is associated with greater energy expenditure through non-exercise-activity thermogenesis (NEAT)[98]; and (3) daily variation in circulating plasma ghrelin, an orexigenic hormone, differs significantly in obese adults pre- and post weight loss. Post-weight loss ghrelin levels are elevated at all time points, stimulating appetite.[99]
While energy intake must be lower and expenditure higher in order to maintain weight loss, the NWCR research supports the heterogeneity of weight-losers and their weight loss methods. Although the weight loss methods have varied, the maintenance strategies are very similar: (1) most consume a low-fat diet and are aware of caloric intake; (2) they self-monitor, including weigh-ins at least once a week, and record food and activity logs; (3) 78% eat breakfast 7 days a week; and (4) they maintain consistently high daily physical activity levels. Diet consistency appears to be important for maintaining weight loss; this includes weekends and holidays.
A high physical activity level may be the primary reason for the success found among NWCR participants, rather than long-term dietary restriction. Ninety-one percent of participants incorporated high levels of activity into their daily routine (28% relied on walking alone and 50% combined walking with other exercises), with the average caloric expenditure approximately 2700 kcal/week, equal to 60-90 min/day. Time in sedentary behaviors, like TV time, was also much lower than the national average, as 97% watched less than 20 hours a week vs the national average of 28 hours a week. As TV time and dietary fat increased, NWCR participants regained more weight.
Cluster analysis indicated that 4 different profiles existed within the NWCR: (1) 50.5% were weight-, health-, and exercise-conscious, monitoring themselves regularly; (2) 27% achieved weight loss but needed extra support; (3) 13% only needed to be told what to do, did it, and succeeded the first time; and (4) 4% were older, less healthy, more likely to eat fat, skip meals, and less likely to exercise. At 3 years, the statistics indicated that environmental influences affect weight losers, as the curve is slightly skewed to the right, indicating gradual weight regain in many individuals.
Preliminary ethnographic studies link behaviors with other important tasks, such as walking as a spiritual time or to connect with friends. Often a new environment was created by changing to food- or activity-related careers, or reinventing social circles to support their new weight. These analyses may offer insight into the success of various methods that promote the significant behavioral changes required to promote weight loss and reduce weight gain in a heterogeneous group.
