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New research reveals that high-fat diets can impair memory and make our immune systems attack our own bodies.
A junk food diet is clearly not healthy. Burgers widen our waistlines, raise our cholesterol levels and tighten our arteries. But scientists now think that even before it shows up as additional pounds on the scale, junk food is changing our bodies in other, surprising ways. It’s actually a form of malnutrition that could be making our immune systems attack our own bodies.
In a recent study published in the Journal of Immunology, scientists at Australia’s University of New South Wales investigated a typical western diet—one that’s high in saturated, monounsaturated and polyunsaturated fatty acids. Specifically, they looked at the diet’s impact on immune cells called T lymphocytes, or T cells.
The researchers fed mice a high-fat diet for nine weeks to see what effect it would have on the T cells before the mice gained weight. The results surprised study leader Abigail Pollock. “Despite our hypothesis that the T cell response and capacity to eliminate invading pathogens would be weakened we actually saw the opposite: the percentage of overactive T cells increased,” she explained.
This might sound great, but having more T cells doesn’t necessarily mean your immune system is stronger. In fact, when the immune system goes into overdrive, it attacks healthy parts of the body, resulting in autoimmune diseases like type 1 diabetes, rheumatoid arthritis and inflammatory bowel disease.
Cell membranes—the bags that hold cells together—are made up of layers of fatty lipid molecules. Looking closely at the T cells, the scientists found that having extra fats in the diet actually changed the amount of lipid molecules in the cell membrane, which in turn, said Pollock, “changes the structure of the cell, altering the responsiveness of the T cells and changing the immune response.”
The team had shown previously that altering the lipid content of T cell membranes affects how they signal and activate each other, but this is the first time the effect has been shown in a living animal. More research is needed, they say, to figure out exactly what’s happening and determine which fats we could avoid to make sure our immune systems don’t go into overdrive.
Indeed, this is not the first study to show that a high-fat diet impacts the immune system; almost 20 years ago, scientists at the University of Oxford in the U.K. studied rats on diets rich in different fats. They found that the lymphocytes of rats fed a high-fat diet rich in palmitic acid grew more, whereas natural killer cells—another type of immune cell—of rats on a high-fat diet rich in stearic acid grew much less.
More recently, scientists at the University of Ulsan in South Korea compared obese mice on a high-fat diet and non-obese mice on a normal diet, and found that the obese mice had significantly lower levels of immune cells, including T cells, in their lymph nodes, where the immune cells wait until they are needed by the body. The lymph nodes near the intestine were much lighter in the obese mice and contained far fewer T cells than those of the control mice.
The scientists concluded that the accumulation of fat around the organs—visceral fat—due to a high-fat diet causes cells in the lymph nodes to self-destruct: “Dietary fat-induced visceral obesity may be crucial for obesity-related immune dysfunction,” they explained.
A high-fat diet won’t only affect your immune system; it could also impair your memory—and that of your kids. When they fed pregnant mice a diet high in lard, scientists at Capital Medical University in China found that the fat in their offspring’s brain was altered. The authors explain in their study: “Our research demonstrated that long-term high lard diet […] changed the brain fatty acids composition and damaged the memory and learning ability of mice.”
What’s in your burger and fries?
A junk food diet is rich in fat, but there are all sorts of other harmful things lurking in there too. Firstly, junk food is highly palatable—it tastes good. This makes us eat more and more, which is an even bigger problem because it’s also very high in calories. A small cheeseburger is 300 calories, the same as a whole (nutritious) meal. And you would rarely just eat a cheeseburger; adding fries (230 calories) and a soda (170 calories) takes the total to a whopping 700.
An excessive calorie intake leads to obesity, which has an impact on the immune system. Norwegian researchers found that being overweight led to inflammation—a sign of an overactive immune response. They studied this on a molecular level, to establish a link between metabolism, inflammation, heart attack and stroke. Their theory is that overeating provides our cells with too much energy and the tiny cellular engines—mitochondria—can stall…