Now, "metabolic damage", or as I prefer to call it, the diet-induced (semi-)permanent down-regulation of our basal energy expenditure wouldn't be a problem if our appetite would decrease to the same degree. Unfortunately, there's a disconnect between appetite and energy expenditure of which a recent study from the University of Leeds suggests that it may be particularly pronounced in the obese.
As J.E. Blundell et al. point out, the prevailing model of homeostatic appetite control envisages two major inputs: (1) signals from adipose tissue and (2) signals from peptide hormones in the gastrointestinal tract. As a SuppVersity reader you are familiar with both inputs - the role of leptin and adiponectin and the satiety hormone induced appetite reduction.
|Figure 1: An increase in energy expenditure increases the already existing correlation between total daily energy intake and the amount of fat-free mass in obese individuals (Blundell. 2015).|
|Nasty Insights into the Yo-Yo-Effect: Lower Body Fat Sticks and the Size of the Emptied Fat Cells May Allow to Creep the Fat Back on| more|
|Figure 2: Changes in resting and total energy expenditure during diet + exercise intervention (Jiminéz Jaime. 2015).|
What decides whether you end up "metabolically damaged" after a diet? We cannot answer this question for sure, but the risk will increase significantly if you lose more than 10% of your original body weight - even if most of the weight you lose is body fat. Eventually, this could be related to the changes in the fill level of the fat cells I hinted at in the red box, but all that is - as of now - not fully experimentally proven. It is yet obvious that genetics will also play an important role - people who are heterogenous for the ADRB2 gene, for example, appear to suffer significantly more pronounced reductions in REE in response to dieting than others (see Figure at the bottom | Camps. 2015). Scientifically sound evidence that you could ameliorate the effect by "reverse dieting", i.e. increasing the energy intake slowly after dieting or dieting down more slowly does not exist.This was not the case in the subjects who didn't adhere strictly to the energy reduced diets. If we take into account that neither of the two groups lost sign. amounts of fat-free mass it is obvious that the mismatch between the theoretically required energy (i.e. calculated based on fat-free mass) and the real energy intake during a diet is mediated by a reduced energy expenditure that could be mediated, at least partly, by a borderline sign. reduction in thyroid function (the reduction in T3 and free T3 Jiminéz Jaime et al. observed didn't reach stat. significance). To become "metabolic damage" this reduction would have to persist even when the subjects returned to an energy sufficient diet.
|Figure 3: Quotient of measured (RMRm) & predicted / calculated (RMPp) resting metabolic rate in subjects after 8w on a protein-enriched formula diet that provided 2.1 MJ/day according to the relative weight change (Camps. 2013).|
- Blundell, J. E., et al. "The Biology of Appetite Control: do Resting Metabolic Rate and Fat-Free Mass drive Energy Intake?." Physiology & behavior (2015).
- Bray, GeorgeA. "Effect of caloric restriction on energy expenditure in obese patients." The Lancet 294.7617 (1969): 397-398.
- Camps, Stefan GJA, Sanne PM Verhoef, and Klaas R. Westerterp. "Weight loss, weight maintenance, and adaptive thermogenesis." The American journal of clinical nutrition 97.5 (2013): 990-994.
- Camps, Stefan GJA, Sanne PM Verhoef, and Klaas R. Westerterp. "Weight loss–induced reduction in physical activity recovers during weight maintenance." The American journal of clinical nutrition 98.4 (2013): 917-923.
- Camps, S. G., et al. "Genetic predisposition and energy restriction induced adaptations in resting energy expenditure and physical activity." How humans economize (2015): 93.
- Camps, S. G. J. A. How humans economize: energy restriction and end energy expenditure. Diss. Maastricht University, 2015.
- Jimenez Jaime, T., et al. "Efecto De La Restricción Calórica Sobre El Gasto Energético En Mujeres Adultas Con Sobrepeso U Obesidad." Nutrición Hospitalaria 31.6 (2015): 2428-2436.