Most people on a diet have weight loss goals. Researchers at Washington University School of Medicine in St. Louis, wanting to study humans instead of mice, offered cash for people willing to gain weight by eating fast food. Participants in the study on diabetes and hypertension discovered that getting fatter faster isn’t that easy.
Differences between rats and humans
Rats, millions of them, are often used in laboratory experiments. However, rats are profoundly different from humans in important ways, making results from rat experiments difficult to extrapolate to humans.
For example, the normal heart rate for rats is between 300-500 beats a minute. Rats are also are very different from humans in the ways their bodies process fat and cholesterol. In rats, the activity of the liver enzyme 5-desaturase, which the body uses to change the chemical structure of fats, is much higher.
Because rats don’t have a gallbladder, bile acids are secreted from the liver directly into the intestine. A rat’s bile acid, called muricholic acid, is also different from humans. Researchers believe muricholic acid allows rats to eliminate cholesterol from their body quicker than humans.
These essential differences make rats, unlike humans, very resistant to changes in blood cholesterol levels and diet induced artery plaques. To cause this damage in rats, researchers must feed them a combination of cholesterol, casein, an anti-thyroid drug and cholic acid (a bile acid). All humans need is fat.
Rapid weight gain
Gaining weight is a gradual process. A pound here, a pound there over a few years adds up to more than a few extra pounds. For an investigation into why some overweight people develop hypertension and diabetes and some don’t, researchers at Washington University School of Medicine hypertension needed real people, not rats, for their study.
But there was a catch. For research purposes, humans participating in the study had to gain weight as rapid as laboratory rats. They offered volunteers cash incentives to add 1,000 calories a day to their diets for three months. Participants could earn up to $3,500 if they gained 5 percent to 6 percent of their body weight during that time period
Fast food pellets
In rat studies, researchers feed the rodents food pellets. It turns out that fast food is the perfect human food pellet. Lead researcher Dr. Samuel Klein told ABC News that because the calories and nutrient content of fast food is always the same, “it’s a very inexpensive, easy and tasteful way to give people extra calories.”
Participants had their extra fast food calories subsidized at McDonalds, Burger King, Taco Bell, Pizza Hut and KFC. Gaining weight fast wasn’t exactly a cakewalk. According to Klein, it was an unpleasant experience stuffing their faces with fast food every day to gain weight rapidly.
No pain, no gain
The volunteers reported feeling awful after a few weeks of burgers, fries, burritos and deep-fried chicken. Some had trouble gaining weight consistently. A few even lost a pound or two and had to eat even more to catch up. Aching knees, sore ankles and shortness of breath were just a few of the complaints heard by the researchers.
The study participants gained weight with a doctor’s supervision. Their health status was carefully monitored along the way. At the conclusion of the weight gain period, they were paid to lose the pounds they gained. They also received diet and exercise counseling.
In addition to the cash, participants may have received an even more valuable benefit from taking part in the study. Many reported that they had lost their appetite for fast food.