Why We Get Fat ... Lessons from Obese Humans & Cafeteria Rats

Vacation bump!  Original Post Date:  3/9/11

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One of the more interesting things (to me) to come out of the "cafeteria rat study" is what the composition of the diet eventually chosen by the rats came out to be.  I'm just going to focus on the SC (standard chow) and CAF (SC + human snack foods) diets in this post.

To recap, the SC had a composition F/C/P of 10/64/26.  When offered this chow along with a rotating selection of three human snack foods from the following list, the rats only ate 15% of their diet as chow (the wording of this is unclear, but their total consumption is ultimately what's important).  The composition of the diet they ended up eating?  CAF was F/C/P of 44/46/10  (note: I've detected slight discrepancies in the numbers here that involve a 1-2% swing in either direction) .  One might think the rodies were only offered fatty snacks, but this is not the case as can be seen in the table below:
 {click to see full size}

The rats likely ate more from about half-way down the list on down in order to get to over 40% fat in their diets.  

We often hear that NHANES tells us Americans are consuming less fat these days (as a percent on average that is true to a nominal extent, but on an absolute basis we consume more) and the majority of the 300 some-odd additional calories we're consuming are carbohydrates.   From this, we are to conclude that it's the "low fat dogma" of replacing fats with carbs that has made us fat.  Somehow us Americans are really taking to heart all of this healthy whole grain, eat what the guvmint tells us to (aka food pyramid) stuff.  

But I think such studies and approximations are somewhat flawed as they are averaged out.  As we can see from the CAF rats v. the SC rats, when exposed to these obesogenic foods, some rats only got a little bigger than the controls - but some got significantly more obese - a few weighed about twice the mass of their counterparts by study end.   

So the 35% reported average increase in consumption masks somewhat the fact that some rats barely ate more while others were eating perhaps even double the amount of others.  When I hear stats like Americans averaging like 80g/day sugar intake I am flabbergasted.  I don't know anyone in my life that eats that much sugar daily, even my husband when he ate more sweets.  (Yes, I'm aware of hidden sugars).  This tells me that we have folks like the former Jimmy Moore who are consuming a ton of sugar and throwing the average. I don't think looking at average consumption for populations provides us with much useful information to determine the cause of rising obesity rates.  Because there are still a ton of skinny folks running around in my circles.   

It is more instructive, IMO, to look at what exactly it is that obese people eat.   To wit we have a study from the LC weight loss realm that monitored the intake of  10 obese subjects (3 men/7 women) in a hospital setting.  For two weeks participants were instructed to consume their "usual diet":

"The clinical research center kitchen provided all food and beverages, and we weighed and recorded everything that was consumed. The food was prepared in the hospital kitchen, as well as in the clinical research center kitchen, and also included foods from local fast food establishments. Participants selected from standard hospital menus each day during their usual diet; participants were also encouraged to request food from the “outside.”  To supplement the hospital menus, we used brand-name foods or fat foods for which nutrient data were available (for example, McDonald’s sandwiches, donuts from Dunkin’ Donuts, and Oreo cookies)."

The intake data from this study is, thus, far superior to dietary recall and self-reported intake.  And, of course, it is ACTUAL intake of obese people, not averaged intake for a population.  Using the means, the Human CAF diet consisted of 3170 calories - 309g carb, 154g fat and 137g protein.  This works out to 44% fat / 39% carb / 17% protein.  

So lower carb than many reducing diets by percentage "by a mile".  The 154g fat on average amounts to 1386 cals - a.k.a. about maintenance or a smidgeon deficit level intake for this post-menopausal woman who has put her metabolism through way too many diet "hoops".   Also a bit higher protein than the CAF rats but otherwise comparable.  

So, when we choose to eat high calorie (usually high fat), low nutrient food, we get fat.  DUH!