Women Can't Go Without Fat, Men Not Without Glucose!? Plus: Could Fat & Glucose Be Created Equal(ly Important)?

Image 1: Are we missing the cacao (=fat) for the chocolate? Study suggests that women do better without glucose than men (img. stern.de)

Ladies, I know I am neglecting you. Testosterone here, bodybuilding there and rarely something about your issues. In the end, it is not fundamentally different with today's news, but the study we are going to look at today is at least food (all pun intended) for thought for both sexes. In fact, Mallory, one of the few women who has not yet been put off by "half naked bodydbuilding types" (if you don't know what I am hinting at, check out the "Biggest Winner" blogpost) and all the hoopla around the "muscle building effects of testosterone", reminded me that I had stashed away a study on the sex-specific reaction to glucose- and lipid-deprivation by scientists from the University of Cincinatti a few weeks ago for "future reference" - a study with quite remarkable results (Sandoval. 2012).

"Gimme those extra sweet twinkies, honey!"

One of the common diet-related clichés is that while men love their greasy barbecue, women just can't live without their chocolate. If we disregard the actual macronutrient content of these foods and go just by their taste, this cliché tells us that women are "carbo-" and men "protein-o-fat-o-holics" - or put simply: Common wisdom would suggest that men are made for low-carbing, while women are going to have a tough time without their sweet treats. The results of the aforementioned study by Sandoval et al. do yet indicate that, from a merely physiological perspective, the exact opposite should be the case... but let's tackle one thing at a time.

Figure 1: Low carb and low fat extreme. By force-feeding the rodents 2-deoxyglucose (2-DG) or mercaptoacetate (MD), the scientists effectively blocked the use of glucose or fatty acids, respectively.

What the scientists did was take a couple of male and female rats and force-fed (IP dosing) the animals with either 80, 250 or 750 mg/kg of 2-deoxyglucose (Figure 1, left) or 115, 200 and 355µmol/kg mercaptoacetate (Figure 1, right). With the former being a "unusable" form of glucose and the latter being a fatty acid that is not susceptible to mitochondrial oxidation, the treatments hamper the use of glucose or fatty acids as a fuel and result in a dose depend glucose or fatty acid deprivation state. In a way this is like jamming the fuel pipe of a car - no matter how much gasoline you put into your tank the engine is not going to be able to use it... similarly, no matter how much carbohydrates, respectively fats the rodents would eat, their "hunger" for glucose of fatty acids would not be satisfied.

No, what would conventional wisdom tell us, should have happened? Right! The female rats would have gone crazy in the 2-DG trial (without their "sweet" glucose) and the male rodents would have gone on one of the infamous "hunter and gatherer" greasy meat binges... but in fact, the exact opposite was the case.

Figure 2: Relative food intake of male and female rats in the 3h after the IP injection of 80, 250 and 750mg 2-deoxyglucose (data adapted from Sandoval. 2012)

As the data in figure 2 shows, the "binge response", i.e. the overeating in response to the artificially induced glucose deprivation, was more pronounced (+170% food intake) and was triggered at lower doses of 2DG (meaning that there was still more glucose available) in male than in female rats. In the mercaptocetate fat deprivation trial, on the other hand, ...

[...] the males significantly increased food intake over saline only in response to the highest dose of MA used [...] In contrast, compared with saline, females had significantly greater
food intake at 115 and 355 µmol/kg, and a strong trend (P < 0.06) at the 200µmol/kg doses of MA.

These findings are not only of interest, because they may shed some (albeit counter-intuitive) light on why men and women tend to "diet" differently, but also because they strongly suggest that we are not dealing with either lipo- or glucostatic controls of energy intake (and probably metabolism), but with both. 

No-carb or no-fat? In the end neither will work

Image 2: Everyone understands that Micheal Phelps seems to understand that he/she cannot eat as many carbs as Michael Phelps (img. Fox), but more and more people fail to realize that they can, ... and for many even, that they must eat more carbs than a sedentary 200lbs overweight type II diabetic.

Despite the fact that he male rats overate "earlier"* to glucose and the female rats "earlier"* to fat deprivation (*earlier means at an overall higher availability of the respective nutrient), when a given threshold was surpassed, both sexes did react with eating everything in sight. In other words, if these results apply to humans as well (2DG studies by Davis et al. would suggest that they do; cf. Davis. 2000), it does not matter if you starve yourself of fat or the ostensibly dispensable and fattening glucose, you still starve and if there is anything everyone should by now have understood, then this: Nothing stalls healthy weightloss more effectively than starvation.

So, don't be a bigoted pighead and acknowledge the value of both, fat and carbohydrates not as mutually exclusive, but as synergistic and with an "optimal" that is in constant flux and will be determined not only by your sex by, but also by your overall, metabolic and endocrine health, by your body composition, by your activity level and the type of activity and many other physiological, psychological, seasonal and environmental parameters that are just as diverse for each of us as our "optimal" macronutrient ratios.