Friday, December 9, 2011

Do you eat like a lab rat?

Like you, Rattus norvegicus enjoys snack cakes

Are you living the rat race? If you labor alone, yet have little privacy, find your work unrewarding, and your lifestyle stressful, get little exercise, fresh air, or fresh food, and find your weight is also slowly climbing, you might be living like a lab rat.

Rattus norvegicus 101

Rats are not mice, and mice are not men. Lab rats are larger than their wild relations, and much larger than house mice. Wistar rats, one of the most common lab rats, weigh 300-500 grams on average as adults, depending on their sex. By comparison, a typical house mouse weighs only 10-25 grams.

Lab rats live in boring, confined, sedentary, lonely conditions, where food is the only constantly available reward. In controlled studies on diet, standard lab rats are typically fed ad libitum, or free-fed, on a standard rat chow. Under these conditions, rats steadily gain weight.

In a fifteen-week study on the so-called “cafeteria diet,”[1] rats fed ad libitum on standard chow gained almost their entire starting weight, from an average starting weight of 300 grams to over 550 grams (see Fig 1e).  

Rats living in the wild are rarely found weighing over 500 grams. The weight gain of lab rats on fairly boring, but unlimited diets is the baseline effect of living like a lab rat. So what happens if you switch to a low-fat formula?

Messing with the formula

Rats fed either a high-fat chow (HFC), or a low-fat/added sugar chow (LFC), both gained weight more quickly than the rats fed a standard formula (SC). You can see by the graph that, while both the high-fat and low-fat fed rats gained more weight on average, the tight clusters in the chart spread out noticeably on both of these modified feeds. This means that there was more variation among individual rats in their response to being switched from standard chow to a new formula. The new formula was either higher in fat or in sugar, suggesting higher palatability.

Those eating the LFD ate the most sugar, even more than rats with unlimited access to snack foods. The researchers also noted that the rats initially eat more of the new food, but by week two, their consumption declines to a level of mild overeating that remains steady through the remainder of the study.

What is the “cafeteria diet”?

But this study wasn’t just on what happens when you change the standard chow. The real test group in this study were those receiving what the researchers call a “cafeteria diet” (CAF). This group of rats got standard rat chow, ad libitum. They also had snack foods, more than they could possibly consume. Three different kinds of snacks, rotated for variety (a full list of the snacks, which included items such as wedding cake and Doritos, is here), were available each day in large quantities. As the researchers write, “this diet engages hedonic feeding.”

The rats in the CAF group naturally disdained most of their standard chow in favor of the tastier snack foods. They ate markedly more food than any of the other rats, and continued doing so even after the two modified-feed groups (HFC and LFC) adjusted their food intake after the second week. Those eating the CAF diet of standard chow plus snack foods continued to eat about half again as much food by weight as those on standard chow alone, and gained weight at about twice the rate. That’s some energy-dense food. These were the heaviest rats at the end of the fifteen weeks, averaging around 750 grams: two and half times their starting weight, and half again as big as the largest wild rats.

What happens when you put humans on a cafeteria diet?

Human volunteers—lean, adult men—allowed to eat whatever they wanted from refrigerated vending machines overate by about 50-60%, just like the rats. The resulting weight gain was about five pounds for each of the volunteers in a one-week study. [2]

As in the rat study, the humans were confined, had few opportunities for recreation, and were constantly observed. The rats, like the humans, were confined in pairs. The humans typically ate alone; no mention is made of the social dining habits of lab rats.

The food that they ate was not exactly the same. While the so-called cafeteria diet that the rats were placed on in the Obesity study was made up of standard rat chow plus an abundance of snack foods, the humans were not offered any kind of standard human chow: no rice, kale, and beans or poached chicken breasts over green salad; no meal replacement bars. Instead, they got all of their food from a set of refrigerated vending machines, stocked with commercially prepared foods. A full list is included in Table 1 of the 1992 American Journal of Clinical Nutrition study: note that the only fresh fruit or vegetable the human volunteers got all week was apples. The foods available were items such as white bread and chicken pie, as well as rat-approved snack foods like cake and Doritos. There were no green vegetables in any of the meals, and very few vegetables or fruits in any form.

Of rats and men

Among the differences between the human and rat studies above, the first, of course, is that humans are not rats. The second is that there was no standard chow available to the humans, only hyperpalatable food, while the rats had access to both. The third is the duration of the study.

Presumably, humans will also adjust to their diets, even if they are eating from vending machines. No one could maintain a lifestyle in which they gained five pounds a week for very long: that’s a hundred and ten pounds a year. Since it’s so difficult to get human volunteers to agree to longer studies, it hasn’t been well documented whether laboratory humans will make the second week adjustment the same way that laboratory rats do.

What’s the difference between your rat race and a rat’s?

Studies on the so-called cafeteria diet are really on the effects of food deserts and the stress of confinement. When all we have is food to reward us in our dingy, artificially-lit cubicles, we gain weight and overeat. Switching from standard commercial fare to a low-fat version, or even to a high-fat version, doesn’t help matters. And when we have really sweet and fatty food as our only reward in life, we eat even more of it.

Humans can insert consciousness, as my therapist likes to say. We can examine our motivations for eating out of pleasure or emotion rather than hunger, and decide whether to proceed or not. Whether to pull the emotional lever. Rats can’t do that. They will go for it, every time.

You can get out of your maze. Your food doesn’t have to come out of vending machines. Your only food options are not chain restaurants and commercial packaged foods, with the odd highly-shippable iceberg lettuce wedge or conventionally grown apple thrown in as a concession to health.  You can cook your own food from fresh ingredients. You can exercise and seek out other stimulating activities that engage your hedonic circuits.

You are not a rat, and you are not trapped.