High-Fat Diet: Putting Research in Context

Gretchen Becker Health Guide
  • My driveway is challenging in the winter: steep, with a sharp dropoff on one side and no guardrails. So I try to keep it “sanded” with ashes from my wood boiler.


    Once some years back, we had a lot of ice and I ran out of ashes. I could have hired someone to spread sand, but that’s pretty expensive. My mother had several woodstoves and didn’t use the ashes, so I took a big grocery bag of ashes (no, they weren’t still warm) from her house and stuck it in the back of my car.


    On the way home, I stopped to see a friend, and for some reason we opened the trunk. She saw the bag and said, “What’s that?”

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    “Oh, it’s my mother’s ashes,” I replied. “I’m going to spread them on the driveway.”


    My friend looked stunned and went white as a pillowcase. Then I realized what she thought I meant and explained that they were from her woodstove, not a crematorium, and we both laughed.


    It’s a good illustration of how important context is to what you say or read, and this is so true with the popular science stories we’re bombarded with every day.


    One example is the term high-fat diet. If you’re eating mostly fast food, greasy burgers and fries, you’re on a high-fat diet, but you’re eating fat in addition to the large amounts of carbohydrate that are in the standard American diet, often referred to as SAD. This is not healthy, and eating this type of high-fat diet is apt to make you fat as well as triggering other conditions like heart disease.


    But if you’re eating a lot of fat instead of carbohydrates, in other words, if you’re on a low-carb, high-fat diet, often written LCHF, the results will be different. Most people find fat satiating, so on such a diet you’re apt to eat less, and this will help you lose weight. And research has shown that limiting carbs creates a metabolic state that has a positive effect on metabolic health even though the fat content of the diet is high.


    Thus it’s very important to know if the high-fat diet referred to in any research paper was obtained by adding fat to a regular diet--the SAD in humans and standard chow in mice--or if it was substituted for some other component. Unfortunately, the news stories often don’t say. And if you try to access the original papers, you discover that the abstract doesn’t say either, and it costs a lot to buy the full text.


    The same context-dependent meaning is true for other terms like high-protein diet. That’s what they used to call the Atkins diet. Now most people are calling Atkins a high-fat diet. But what does high mean? The total amount of protein or fat or the percentage of the nutrient?


    Let’s say for lunch you used to have a burger and fries. You go on a low-carb diet and reject the bun and the fries. That means you’re eating fewer calories, but even though you’re eating the same amount of protein, you’re eating a higher percentage of protein because you’re not eating any of the carbs. Percentages don’t mean much if you don’t know the total amounts.


    Other variables are also important, for example, whether some study was done in mice, dogs, or humans. Or whether a “Mediterranean diet” means lots of fish and fruits and vegetables or lots of pizza and spaghetti. Or whether a study of exercise involved obese middle-aged people with diabetes who walked for 10 minutes a day for 3 weeks or healthy slim college students who ran for 2 hours every day for several months.


    They say rules are meant to be broken, and generalizations are broken when they’re not put into context. A recent story making the rounds has no context. The popular press story doesn’t define the “high-fat diet” or the “balanced low-fat” diet they say was beneficial. The author of the paper, Paolo Sassone-Corsi, kindly sent me a copy of the full article and I was able to research what the mice actually ate: a popular mouse high-fat diet (Research Diets D12492)  that contains 20% carbohydrate, 60% fat, and 20% protein. The carbohydrate is maltodextrin and sucrose, both high-GI carbs.

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    In a human on a 2000-calorie-a-day diet, 20% would be 100 g of carbohydrate, so the diet would not be considered very low carb, or ketogenic, even though it would have less carbohydrate than a “normal” diet or the control rat chow. And the effects of fat when a mouse is on a ketogenic diet are different from those when they’re eating more carbohydrate. Yet the average reader will conclude that fat is dangerous.


    Another example of information taken out of context is a study that concluded that taking vitamins is useless and might even be dangerous. The researchers followed people who had had a heart attack and found that in five years, those who took vitamins had no fewer incidents of a second “hearth [sic] attack.” Another study of Alzheimer’s disease had a similar result. As did a study of cardiovascular disease, cancer, and mortality in general.


    So a professor at Johns Hopkins medical school said, “Supplementation with extra vitamins or micronutrients doesn’t really benefit you if you don’t have a deficiency [italics mine].” And then they list some exceptions: elderly people and vitamin D, young women and iodine, and Mexican-American women and young children and iron.


    But no one will remember the exceptions. They’ll remember the headlines, like “Enough Is Enough: Stop Wasting Money on Vitamin and Mineral Supplements” in the Annals of Internal Medicine.


    One problem people with type 2 diabetes face is that most of us would like to lose weight, and that usually means cutting back on food. If you’re eating 3000 calories a day, including lots of fruits and vegetables, you’re most likely getting enough vitamins and minerals from your food (if you’re eating 3000 calories of white bread and burgers, you might not be). But if you’re eating closer to 1000 calories, maybe even less if you have real difficulty losing weight, you could have a deficiency of some nutrient. If you’re elderly and don’t have much appetite because you can’t exercise, again, you might also have a deficiency of some kind.


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    This study is fine if you read it carefully, in context. If not, like the woman hearing about the ashes on the driveway, you might come away with the wrong idea.

Published On: December 29, 2013