By Anna Drangowska-Way
I am rushing for another meeting. My stomach is grumbling. I don’t have time to eat a proper lunch, I think, just as the sweet smell of the bakery hits me. Maybe I can just grab it to go, I think. I always eat so healthy —one “cheat food” a day is fine. In a moment I’m in the store, ordering a hot chocolate and a doughnut. I swipe away the guilt. You’re not gaining weight, so don’t worry.
But is there really no reason to worry? Research in rats calls that idea into question.
In a recent study, rats fed high-fat and high-sugar junk food for only one hour per day had increased levels of cholesterol and sugar in their blood and livers, compared with rats that ate only healthy food. In people, such metabolic changes are often precursors of serious illnesses such as diabetes and cardiovascular disease.
Researchers at three Italian universities compared three groups of rats. One group had unrestricted access to junk food for 40 days. Another group could consume the same junk food, but only for one hour a day. And the third group ate only healthy food. The three dietary conditions were, for the rats, similar to a person eating all their meals and snacks in fast-food restaurants, versus mostly eating healthy but indulging in a junk-food snack about once a day or skipping meals to make up for indulgent eating, versus eating only healthy meals. The study is reported in the July issue of the FASEB Journal.
The researchers expected that unlimited access to the junk food would cause rats to gain weight, as well as trigger unhealthy metabolic changes, says Anna Maria Giudetti, a biochemist at the University of Salento, who led the study. The team was less sure how more restricted consumption of junk food would affect metabolism.
As the researchers expected, rats that could gorge themselves all day on junk food had, on average, 20 percent higher body weight at the end of the experiment than rats on a healthy diet. Rats that consumed junk food for only one hour had similar body weight to rats that ate a healthy diet.
But that doesn’t mean they got away unscathed. Although the animals that ate junk food for only an hour a day had similar body weight as rats on healthy diet, they showed significant differences in blood sugar and cholesterol. Blood sugar levels in animals with restricted access to junk food were 25 percent higher, and levels of “good” cholesterol in their blood were 25 percent lower that of rats on a healthy diet. Additionally, their levels of total cholesterol in their liver were double compared with those of rats on healthy diet. These metabolic effects were similar to what the animals on an unrestricted junk-food diet experienced.
In general, rats' metabolic systems correspond closely to humans'. However, as Naïma Moustaïd-Moussa, a nutrition and obesity scientist at Texas Tech University who was not involved in the study, points out, although rats and humans have similar fasting glucose levels, their baseline levels of “good” and “bad” cholesterol differ. But for the purposes of interpreting the new study, Moustaïd-Moussa says, what’s important is not the rats’ absolute lipid levels, but how different dietary patterns affect those levels. Rats and humans would likely respond similarly in this respect, she says.
The results suggest that maintaining proper weight is not everything, says Silvana Gaetani, a neuropsychopharmacologist at the Sapienza University of Rome and one of the study co-authors. Instead, Gaetani says, we need to think about our health in broader terms. Restricting food and not paying attention to adequate food choices can give the “wrong impression” that as long as you’re not gaining weight, your diet must be safe. But doing so, she says, is like “when you clean and you put the dust under the carpet.”
Moustaïd-Moussa agrees. “Sometimes we focus too much on weight,” she says. “Yes, when you lose weight you get benefits.” But, she says, “We have to move beyond the weight.” Future research, she suggests, should tease out which components of the rats’ junk-food diet — high sugar or high fat, and if fat, which type of fat — caused the adverse metabolic changes. And since some people don’t want to give up eating junk food altogether, it will be valuable to know how much people can benefit from making partial dietary changes. For example, what would happen if you add fish oil to your otherwise unhealthy diet? Addressing such nuances, Moustaïd-Moussa says, will be important for extrapolating from the new results to make dietary recommendations.
Anna Drangowska-Way, M.Sc., is a Biology Ph.D. student at the University of Virginia. She wrote for biotechnologia.pl and she has completed the National Association of Science Writers’ David Perlman Virtual Mentoring Program. E-mail her at annadrangowskaway@gmail.com and follow her on Twitter @drangowska.
This story was produced as part of NASW's David Perlman Summer Mentoring Program, which was launched in 2020 by our Education Committee. Drangowska-Way was mentored by Siri Carpenter.
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