Saturday, April 14, 2012

The Diet Trap Revisited: Yo-Yo Effect, Decreased Basal Metabolic Rate and the Myth of Fat-Free Mass Losses. Plus: Gender Discrimination and the "Diabetic Advantage"

Image 1: Geoffrey Cannon's "Dieting Makes You Fat" was first published in 1983 and has lost nothing of its topicality.
According to relatively recent data (Bendixen. 2002; Kruger. 2004), roughly 30–50% of the women and 10–30% of the men are currently or have recently attempted to lose weight by "dieting". I would assume that at least 90% of these dieters followed did so by just following the "Hippocratic approach" to weight loss of eating less and exercising more a strategy that is probably even more futile today, than 400BC, when it was first proposed by the father of modern allopathic medicine (cf. Precope. 1952), or 1983, when Cannon and Einzig published the first of the countless editions of their explanation for why dieting is a disaster (which is  by the way, not just because a calorie was not a calorie ;-).

Dieting makes you fat - fullstop!

From earlier as well as more recent studies on the effects of starvation, calorie restriction and exertional physical training, sleep and energy deprivation during boot camp like activities in the army, we know that prolonged caloric restriction and/or exercise induced energy deficiency will lead to hyperphagia and a subsequent "fat overshoot". As the data in figure 1 goes to show, the latter can be pretty profound and ranges from +2.7kg in the seminal fasting study by Benedict from 1907 up to 6.5kg in the well-powered (n=700) food rationing study, Fleisch et al. conducted after WW2.
Figure 1: Fat gain (in kg) after fasting, restricted eating and boot-camp like training in an energy deficit (left) and lean mass and fat loss and regain in the Minnesota experiment (data based on summary by Dullo. 1997 and  Keys. 1950)
A very similar scenario was also simulated in the so-called Minnesota experiment by Keys et al. (Keys. 1950) in the course of which thirty-two healthy volunteers were kept on semi-starvation diets for 12 weeks. During the subsequent 12 weeks their caloric intake was gradually increased until, for the last 8 weeks of the study, they had free access to food. From A brief glimpse at the data in figure 1 (right) should suffice to be able to tell that this type of "controlled re-feed" despite being conducted over a 12-week period did not prevent the +80% body fat overshoot in the subsequent ad-libitum feeding phase - and that despite the fact that the total caloric intake of the subjects had returned to baseline in week 7 of the ad-libitum phase (after temporary overshoot of up to +60% in week two, though).

Did you try to lose weight in puberty? Well that's the reason you are fat, now.

A 1999 study by Stice et al. shows that it does not even take a 12-week period of restriced eating (-50% in the Minnesota experiment) to get caught in the vicious circle of yo-yo dieting. For the 692 female teenagers from the ninth grade of a a Californian high school, even the allegedly harmless "I got to get in shape for spring" diets, were associated with a statistically significant shift in  the onset of obesity (Stice. 1999). With anxiously monitoring your caloric intake and being only marginally less detrimental than actual dieting:
  • caloric restraint: +192% increased chance of early obesity (p < 0.001),
  • dieting (self-labeled): +224% increased chance of early obesity (p < 0.01),
  • exercise or weight control: +25% increased chance of early obesity (p < 0.01)
  • (ab)use of laxatives / appetite suppressants: +85% risk of early obesity (p < 0.1)
In this regard it appears to be somewhat unfair that women are not only more susceptible to the diet trap due to the bad role models and ill advice they are presented with on a daily basis (cf. "Strong is the Better Sexy! Female Athletes as Role Models"), but - as the recent re-evaluation of existing data on the effects of dairy and/or calcium rich diets and resistance training on weight loss in 72 obese(BMI 33.4kg/m², 38.8% body fat) middle-aged (56y) caucasian men and women would suggests (Soares. 2012) - also suffer from a significantly more pronounced reduction in basal metabolic, and more importantly fatty acid oxidation rate after weight loss (-5.2kg fat; -2.3kg lean mass).
Figure 2: Basal metabolic rate (BMR) fatty acid and carbohydrate oxidation rate (FOR, COR) before and after weight loss interventions in subjects with and without metabolic syndrome (left); changes in BMR, FOR and COR in male and female study participants (data adapted / calculated based on Soares. 2012)
Irrespective of the sex of the subjects, participants who recovered from metabolic syndrome as a result of their weight loss suffered the greatest reduction in metabolic rate
  • 484kj/day and 414kj/day reduction in the subjects who were either healthy or whose metabolic syndrome did not go into remission vs. 
  • 670kj/day reduction in the "lucky" ones who got rid of their metabolic syndrome (criteria according to Alberti. 2009)
While Soares et al. can only speculate that these gender differences may be related to differences in either glucose or adiponectin metabolism, the initially counter-intuitive finding that the remission of the metabolic syndrome appears to predispose to future weight gain ue to reductions in basal energy expenditure bring the results of another relatively recent study to mind, in which Miyake et al. were able to show that within a cohort of  thirty obese Japanese adults with pre-diabetes (n=7), type 2 diabetes (n=13) or without diabetes (n=10) the diabetic subjects had 7.1% higher basal metabolic rates than the non-diabetic study participants (after adjustment for fat-free mass, fat mass, age, and sex; Myiake. 2011), with a statistically significant correlation between residual BMR and fasting glucose (r=0.391, p=0.032).

The diet trap and the myth of reductions in fat-free mass

Figure 3: Ratio of resting metabolic rate to fat free mass before and 4 and 8 weeks after a protein sparing fast; means, top; individual, bottom (Elliot. 1989)
Overall, these results only confirm the longstanding findings of e.g. Elliot et al. and Weinsier et al. who were able to show that the often touted linear relationship between resting or basal metabolic rate and fat-free mass does not exist - neither in the 1111 non-dieting normal subjects (118 infants and pre-schoolers, 323 adolescents, and 670 adults; Weinsier. 1997) in the Weinsier study, nor in the seven obese women in the Elliot study, who lost an average of 23kg body fat and 5kg of lean mass in the course of an 8-week modified protein sparing fast (Elliot. 1989; cf. figure 3).

So, no matter how you look at it, classic dieting may make slimmer in the short run, but whenever larger caloric deficits and faster weight loss come into play (irrespective of the amount of lean muscle you may lose), caloric restriction and exercising just to lose weight, are going to set you up for a fat rebound!