In Pursuit of a Biomarker of Weight Gain Susceptibility-Is FGF21 a Candidate?

Protection against overfeeding-induced weight gain is preserved in obesity but does not require FGF21 or MC4R

Overfeeding triggers homeostatic compensatory mechanisms that counteract weight gain. Here, we show that both lean and diet-induced obese (DIO) male mice exhibit a potent and prolonged inhibition of voluntary food intake following overfeeding-induced weight gain. We reveal that FGF21 is dispensable for this defense against weight gain. Targeted proteomics unveiled novel circulating factors linked to overfeeding, including the protease  legumain (LGMN). Administration of recombinant LGMN lowers body weight and food intake in DIO mice. The protection against weight gain is also associated with reduced vascularization in the hypothalamus and sustained reductions in the expression of the orexigenic neuropeptide genes, Npy and Agrp, suggesting a role for hypothalamic signaling in this homeostatic recovery from overfeeding. Overfeeding of melanocortin 4 receptor (MC4R) KO mice shows that these mice can suppress voluntary food intake and counteract the enforced weight gain, although their rate of weight recovery is impaired. Collectively, these findings demonstrate that the defense against overfeeding-induced weight gain remains intact in obesity and involves mechanisms independent of both FGF21 and MC4R.

What Is the Impact of Energy Expenditure on Energy Intake?

Coupling energy intake (EI) to increases in energy expenditure (EE) may be adaptively, compensatorily, or maladaptively leading to weight gain. This narrative review examines if functioning of the homeostatic responses depends on the type of physiological perturbations in EE (e.g., due to exercise, sleep, temperature, or growth), or if it is influenced by protein intake, or the extent, duration, timing, and frequency of EE. As different measures to increase EE could convey discrepant neuronal or humoral signals that help to control food intake, the coupling of EI to EE could be tight or loose, which implies that some ways to increase EE may have advantages for body weight regulation. Exercise, physical activity, heat exposure, and a high protein intake favor weight loss, whereas an increase in EE due to cold exposure or sleep loss likely contributes to an overcompensation of EI, especially in vulnerable thrifty phenotypes, as well as under obesogenic environmental conditions, such as energy dense high fat—high carbohydrate diets. Irrespective of the type of EE, transient elevations in the metabolic rate seem to be general risk factors for weight gain, because a subsequent decrease in energy requirement is not compensated by an adequate adaptation of appetite and EI.

Low capacity to oxidize fat and body weight

For a given positive energy balance, a low capacity to oxidize fat could contribute to weight gain (low fat oxidation hypothesis). This hypothesis is based on the arguments that for a given stable diet and food quotient (FQ), the respiratory quotient (RQ) is higher in obesity prone (OP) than in obesity resistant individuals (OR) and that a high RQ predicts higher future weight gain. A review of 42 studies shows that there is no convincing experimental support to these arguments and thus for the low fat oxidation hypothesis. A power analysis also shows that this hypothesis might be impossible to experimentally confirm because very large numbers of subjects would be needed to reject the null hypotheses that the 24-h RQ is not different in OP and OR or that future weight gain is not different in individuals with a low and high 24-h RQ at baseline. A re-examination of the significance of the 24-hour and fasting RQ also shows that the assumption underlying the low fat oxidation hypothesis that a high RQ reflects a low capacity to oxidize fat is not valid: For a stable diet, the 24-h RQ entirely depends on FQ and energy balance, and the fasting RQ mainly depends on the FQ and energy balance and on the size of glycogen stores.

Metabolic response to fasting predicts weight gain during low-protein overfeeding in lean men: further evidence for spendthrift and thrifty metabolic phenotypes

BACKGROUND

Greater increase in 24-h energy expenditure (24EE) during overfeeding and smaller decrease in 24EE during fasting ("spendthrift" metabolic phenotype) are associated with more weight loss during sustained caloric restriction in overweight subjects.

OBJECTIVES

The aim of this study was to investigate whether these acute metabolic responses can also predict weight gain during sustained overfeeding in lean individuals.

METHODS

Seven lean men participated in this study. Prior to overfeeding, 24EE responses to fasting and 200% normal-protein overfeeding were measured in a whole-room indirect calorimeter. Volunteers underwent 6 wk of 150% low-protein (2%) overfeeding followed by another wk of weight-maintaining diet, during which 24EE was revaluated. Body composition, 24EE, and various hormone concentrations, including fibroblast growth factor 21 (FGF21), were assessed at baseline, at wk 1, 3, and 6 of the overfeeding period, and 1 wk following overfeeding through the use of dual-energy X-ray absorptiometry, indirect calorimetry, and ELISA. Cumulative energy surplus was calculated from 24EE, daily physical activity, and direct measurements of calories of nutrient intake, feces, and urine by bomb calorimetry.

RESULTS

The average weight gain during 6 wk of low-protein overfeeding was 3.8 kg (6.1%, min: +2.5%, max: +8.0%). During 24-h fasting at baseline, 24EE decreased on average (mean ± SD) by 158 ± 81 kcal/d (P = 0.007). Subjects with less 24EE decrease during fasting (more metabolically spendthrift individuals) gained less weight (r = -0.84, P = 0.03), less fat mass (r = -0.81, P = 0.049), and stored less calories (r = -0.91, P = 0.03) during overfeeding. Following overfeeding, increased 24EE above requirements for achieved body size was associated with less weight and fat mass gain (r = -0.78, P = 0.04) and with the increase in 24EE during 200% normal-protein overfeeding measured at baseline (r = 0.91, P = 0.005). Serum FGF21 concentrations increased up to 44-fold during overfeeding (P <  0.0001).

CONCLUSIONS

Low-protein overfeeding may be an important tool to identify metabolic phenotypes (spendthrift compared with thrifty) that characterize susceptibility to weight gain. This trial was registered at clinicaltrials.gov as NCT00687115.