Eating Fat Does Not Make You Fat

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Mark Hyman, MD, is a functional medicine doctor and best-selling author of 12 books. He is also the director of the Cleveland Clinic Center for Functional Medicine, the Pritzker Foundation Chair in Functional Medicine at the Cleveland Clinic, the chairman of the Institute for Functional Medicine, and the founder of The UltraWellness Center. Below is an excerpt from his latest book, EAT FAT, GET THIN.

If you believe that all calories are created equal (and you now know they definitively are not), then it stands to reason that you’d also be quick to demonize fat and blame it for weight gain. It seems like simple math: If fat has more than twice as many calories per gram as carbs or protein, then if you eat less fat, you will eat fewer calories and lose weight. Sounds reasonable, doesn’t it? Unfortunately it just doesn’t work out that way for many reasons.

That all calories are the same in terms of effects on your weight and metabolism is one of the most persistent myths in medicine today. They are the same in a laboratory, when you burn them in a vacuum. But not when you eat them. New public policies require restaurants to list the calorie content of each dish, and food companies to label calories per serving in large, bold type. But this is the wrong strategy, because it implies that only calories matter. The truth is that different calories affect your gene expression, hormones, brain chemistry, immune system, metabolism, and even your gut flora differently. While it is helpful to track calories in processed and fast food (because they can be so loaded with bad calories) — it can deter you from eating that 1,200-calorie meal— if you eat real food, you don’t need to track calories.

Metabolism is not a math problem. It’s not about balancing “energy” or calories in and calories out. If it were, and you ate an additional 100 calories a day, which is about a big bite of food, after a year you would gain ten pounds. After a decade you would gain one hundred pounds. This just doesn’t happen. Even if you were the world record holder in calorie counting, you couldn’t get the math right to control your weight.

That’s why weight and metabolism are not math problems. The quality of the food you eat matters much more than the quantity. If food were only about calories, it wouldn’t matter what specific foods you ate, as long as you kept below a certain number of calories. But it does. Why?

Food is not just a source of energy or calories. Food is information. It contains instructions that affect every biological function of your body. It is the stuff that controls everything. Food affects the expression of your genes (determining which ones get triggered to cause or prevent disease) and influences your hormones, brain chemistry, immune system, gut flora, and metabolism at every level. It works fast, in real time with every bite. This is the groundbreaking science of nutrigenomics.

The whole idea that a calorie is a calorie is finally being intensely studied by the Nutrition Science Initiative, 1 headed by Dr. Peter Attia and Gary Taubes (author of Good Calories, Bad Calories). The institute is funding rigorous and larger studies by the world’s best researchers to answer this question once and for all and quiet the naysayers— of which there are still many, despite adequate evidence. They are even enlisting scientists who disagree with their hypothesis that all calories are not equal so those scientists can prove themselves wrong.

This is not a new idea. Nutrition expert Ann Louise Gittleman, PhD, CNS, the former director of nutrition at the renowned low-fat, high-carb Pritikin Longevity Center, was the first in the country to write about the importance of fats in her bestselling Beyond Pritikin, released in 1988. For years, she has been a pioneer and the lone voice in promoting the importance of the right fats. She identified the flaws in the science back then and, in thirty of her books that followed, implored us to eat more fat. Sadly, we ignored her prescient advice.

More and more scientists are confirming that calories coming from fat are better for weight loss and improving metabolism. Kevin Hall, from the National Institutes of Health, has found that in a metabolic ward where every ounce of food and every movement and every calorie burned are carefully measured, those who ate more fat calories (compared to an identical number of calories from carbs) burned more than 100 additional calories a day. Over a year that amounts to a ten-pound weight loss. He also reported that in studies of brain imaging and function, eating more fat shuts off the hunger and craving centers of the brain. It seems that the brain matters most in terms of controlling food intake, taste preferences, and metabolism. And that dietary fat can positively impact the whole calorie-burning process.

Most of us assume that overeating makes us gain weight. That sounds like a reasonable assumption, right? But in a brilliant paper in the Journal of the American Medical Association, Harvard professor Dr. David Ludwig lays out the case for a very different view of obesity and metabolism.

He says, simply, that we have it backwards. It is not eating more and exercising less that makes you fat, but being fat that makes you eat more and exercise less. Essentially your fat cells “get hungry” and drive you to overeat. He describes this process in detail in his book Always Hungry? When you are overweight, your hormones and brain chemistry make you hungry and tired.

This turns all our thinking about weight gain upside down and contradicts every single established recommendation for weight loss. Rather than focus on calories and quantity, Dr. Ludwig suggests we focus on quality and the composition of our diet (amount and type of protein, fat, and carbs) to allow the body’s natural intelligence to regulate hunger, activity, metabolism, and weight. Forget about willpower— use science to cut your hunger, give you energy, and speed up your metabolism!

First, when you try to restrict calories and exercise more, your body is hardwired to perceive a starvation situation. That makes you tired (so you move less and conserve energy) and hungry (so you eat more), and it slows down your metabolism (so you don’t die!). This “eat less, exercise more” formula is not too successful for most people. It can work for a short time, certainly, but less than 10 percent of people lose weight and keep it off for a year; you will almost always rebound and gain back the weight.

Second, when you eat carbs and sugar, insulin spikes and your blood sugar drops. The insulin drives most of the available fuel in your bloodstream into fat cells, especially the fat cells around your middle, otherwise known as belly fat. So your body is starved of fuel, and this stimulates your brain5 to make you eat more. You could have a year’s worth of stored energy in your fat tissue and yet feel like you are starving.

The only thing that can stop this vicious cycle is eating a lot of fat and cutting out the refined carbs and sugar. A high-fat, low-carb diet leads to a faster metabolism and sustained weight loss.


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