by Mark Hyman
The Diogenes Project found that a lower-carb, higher-protein diet worked better for weight loss maintenance.9 Other studies10 and large reviews of low-carb, high-fat diets all show that they are better at aiding weight loss11 and cardiovascular health.12 People also find it easier to stick with these diets because fat makes food more satisfying and taste better.
A very important study published in the Lancet by Dr. David Ludwig compared the effect of a high-glycemic diet vs. a low-glycemic diet on metabolism in rats.13 He found that changes in dietary composition (high-glycemic or changing the ratios of protein, fat, and carbs) produced obesity in genetically normal animals, even when diets had exactly the same number of calories. He fed each group of rats the amount of food that would allow them to maintain identical body weights. The rats fed the high-glycemic diet (high in sugar and refined carbs) gained weight on an identical number of calories. In fact they gained 70 percent more body fat (mostly belly fat) than the rats fed the high-fat diet. They also had lower muscle mass, were hungrier, had higher levels of insulin, and had more cardiovascular risk factors.
Another study on rats fed a ketogenic diet (very, very low-carb and very high-fat) again found that weight loss was greater than in rats fed a high-carb diet, even though they ate exactly the same number of calories.14 The genes that increase fat burning and reduced fat storage were all turned on. The rats on the high-fat diet also increased calorie burning and energy expenditure and reversed pre-diabetes.
That’s great for the rats, sure, but what about people? In human experiments, those who ate the high-fat diets had a much faster metabolism. The low-fat, high-carb diets forced all the food energy into the cells (because of insulin spikes), and this slowed metabolism. The group that ate the higher-fat diet had a faster metabolism, even on the same number of calories.15 That means they burned more calories even when watching TV or sleeping.
Another human study performed by Dr. Ludwig and his colleagues that compared high-fat, low-carb diets with high-carb, low-fat diets in a controlled feeding environment found the same thing.16 This was a “crossover trial”: For half the study participants ate a high-fat, low-carb, low-glycemic diet; then during the other half they ate a low-fat, high-carb, high-glycemic diet. There was also another group that ate a moderate-fat diet. This allowed the researchers to study the effects of different diets on metabolism for each person.
The low-fat, high-glycemic diet consisted of 60 percent carbs, 20 percent protein, and 20 percent fat; the low-glycemic, high-fat diet consisted of 60 percent fat, 10 percent carbs, and 30 percent protein. Calorie content was identical for each diet. The high-fat group ended up burning 300 calories more a day than the low-fat group. The high-fat group also had the most improvements in cholesterol, PAI-1 (which shows the likelihood of having blood clots and heart attacks), and insulin resistance.
We know that there is a lot of bias in the world of science. But the Cochrane Collaboration, a global independent network of researchers, professionals, patients, caregivers, and others interested in health who receive no money from industry and are not affiliated with governments, did a review of low-glycemic diets, which are typically high-fat.17 They concluded that the low-glycemic, high-fat diets did much better than the low-fat, low-calorie diets for weight loss and health. And the final nail in the coffin proving that high-fat diets work better than low-fat diets for weight loss was a review by Harvard researchers of 53 different randomized controlled trials that lasted a year or more. They found that high-fat, low-carb diets, compared head to head with low-fat diets, worked much better for weight loss.18
EATING A LOW-FAT DIET MAKES YOU CRAVE BAD FOODS
When you eat a low-calorie, low-fat, high-carb diet, you want to eat more19 and eat higher-calorie and higher-carb foods.20 Higher-carb foods make you crave even more carbs.
What’s fascinating is that even before people gain weight (and accumulate a lot of those greedy, lazy-making fat cells), they show significant metabolic changes as a result of consuming a higher-carb, lower-fat diet. These changes in belly fat cells start the whole process of weight gain. Body fat, especially belly fat, is not just a bunch of excess baggage storing calories for a later date. Body fat is a complex metabolic tissue that is critical in regulating your appetite, controlling the rate of calorie burning, and regulating weight.
In a clever experiment on a group of schoolchildren, scientists tested the effects of fat and carbs on eating behavior by giving sixth-grade kids either cheese wedges or potato chips. The kids were told they could eat as much as they wanted.21 Both groups were equally hungry at the start of the study, according to standard hunger measures. Based on the idea that you will gain weight if you eat more fat-rich foods, like cheese, which contain more calories per gram of food (9 calories per gram of fat vs. 4 calories per gram of carb), the cheese-eating kids should have consumed more calories. Eat more calories (because fat is more calorie dense), gain more weight. Simple math, right? But it doesn’t work that way in the complex world of biology. If carbs drive you to overeat, the potato chip group should have eaten more calories. What happened? The kids in the potato chip group ate three times as many calories as the kids in the cheese group! And kids who were already overweight consumed even more calories. More evidence that fat cells are “hungry.”
When the cheese was combined with vegetables, the kids ate even fewer total calories. This was more notable in the kids who were overweight or obese. When we combine foods that are high in nutrients, we naturally eat less, even with hungry fat cells. The key here is that nutrient-dense foods (real whole foods) are satisfying, while processed empty foods (nutrient-poor foods) are less satisfying, even though they may contain more calories!
This is consistent with a review of research on carb consumption in kids showing that kids who ate more carbs ate more food and were overall hungrier.22 If you eat a lot of carbs, you are hungrier and take in more overall food and calories in a day than if you eat fat.23
When taken as a whole, the science shows us a clear pattern of evidence that carbs make you fat, while fat makes you thin. Foods like white rice, potatoes, and sugary beverages promote obesity and related diseases. Fat- (and calorie-)rich foods, like nuts, oily fish, and olive oil, and even foods high in saturated fats, promote weight loss and reduce risk of these diseases when you cut out the sugar and refined carbs.
But Wait… What About Studies That Show That Low-Fat Diets Speed Metabolism?
Recently, a study in Cell Metabolism by Kevin Hall from the National Institutes of Heath attracted a lot of buzz in the news and online, as it seemed to prove once and for all that low-fat diets work better for weight loss than low-carb diets. But it did no such thing. There were some real problems with the study, and things that were overlooked by the media reports.
Here are the important considerations:
It was a very short-duration study (only six days) conducted on only nineteen people who were contained in a metabolic ward where all the food was provided; people did not self-regulate based on hunger or appetite, so it was not based on normal everyday experience. It showed what happened in a vacuum but not in real life.
The low-carb diet wasn’t low at all, actually, with 29 percent of calories coming from carbs, including refined carbs. A true low-carb diet would have less than 10 percent of calories from carbs.
The low-fat study contained very low fat (about 7 percent of calories), which is incredibly hard to sustain in real life.
The low-carb group actually did show an increase in fat burning, which is a good thing. But the low-fat group had a higher amount of body-fat loss, which also seems like a good thing. But it was such a short study; other studies show that it takes longer to adapt to a higher-fat diet. Also, other longer-term studies comparing fat and carbs show that a higher-fat diet leads to more weight loss.
A new, big, long-term (one year vs. six days) trial of low-carb, higher-fat diets is currently under way (at the time of this writing) called the CENTRAL trial.24 The prelimin
ary data shows that the low-carb/higher-fat diet had major advantages over the low-fat diet. The high-fat diet improved body composition (more muscle, less fat). It also helped fix fatty liver and reduce dangerous belly or organ fat. The study actually provided part of the food so the study participants stuck with the diet.
Sorry it’s so confusing, but looking at all the evidence and real-life experience, it is clear that in actual humans living in the real world (not as lab rats with their food intake completely controlled), lower-carb, higher-fat diets lead to greater satiety (feeling full), more weight loss, and faster metabolism.
CONCERNS ABOUT HIGH-FAT, LOW-CARB DIETS
My standing line about the Atkins Diet used to be that it works if you don’t mind constipation, bad breath, and kidney failure (due to its high content of animal protein). Atkins focused on fat and protein and not enough on veggies and plant foods. It’s true there are a few concerns worth mentioning if you don’t follow the plan carefully by eating more fiber, vegetables, and salt, like constipation, electrolyte imbalances from low sodium (or salt), dizziness, and muscle cramps—but they are easy to prevent and manage.
When you cut out a lot of grains and beans and eat more fat, your fiber intake can drop. However, on the Eat Fat, Get Thin Plan you will be eating a ton of vegetables, nuts and seeds, and some fruit, all of which contain a lot of fiber. You will also be consuming extra fiber, called PGX. You need to drink 8 glasses of water a day because you will lose a lot of fluid as you detox from all the sugar and processed foods. Those foods are inflammatory and make you retain water, so when you stop eating them you lose water. Also, when you eat less carbs, you burn up glycogen (the sugar stores in your muscle). Since glycogen makes you retain water, when glycogen gets burned up, you lose the water.
When you cut out the carbs you lower your insulin levels. That causes the kidneys to dump salt, or sodium, from your kidneys,25 because insulin causes you to retain salt (and thus water). This can cause muscle cramps. The best solution is to add 1 to 2 teaspoons of salt to your diet every day. And you need more potassium, too (about 2 grams a day); you’ll get this from the vegetable and bone broth I recommend in Chapter 13.
Some of you might worry that lowering your carb intake will affect your athletic performance. Many athletes “carb-load” before a race to replenish glycogen, glucose stored in muscles. However, many studies show that once you adapt to a lower-carb diet, endurance exercise is not affected at all. Anaerobic exercise like sprinting or weight lifting can be affected by lack of glycogen stores, but the carbs in the Eat Fat, Get Thin program will help you keep enough glycogen stores to prevent this problem. It takes a few weeks to adapt to lower-carb, higher-fat eating and to switch your body from carb burning to fat burning, which is what happens when you follow the Eat Fat, Get Thin program. And you need to make sure you eat enough protein—about 1.5 grams per kilogram (0.68 grams per pound) of body weight a day, or about 100 to 120 grams for the average person; eating protein at each meal helps to build muscle. However, too much protein can turn to sugar in your bloodstream if you are not active or exercising, so if you are not active you may need less protein. We’ll talk about this more in Chapter 13.
In the next few chapters, I’ll help dispel some of the other myths and clear up the confusion surrounding fat, both dietary and biological. We’ll get to the bottom-line facts on everything from whether saturated fat causes heart disease (hint: it doesn’t) to which oils are truly good for you and which unhealthy ones stole the spotlight thanks to clever marketing ploys. The way I see it, the way out of this big, fat mess we’re in is through discovering the truth and embracing a way of eating that welcomes back fat as a critical component for weight loss and health.
Beyond Food: Other Causes of Obesity and Damaged Metabolism
John Muir said, “When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” And it is so with human biology. The framework of Functional Medicine is based on understanding the body as a dynamic system where everything is connected, where there is a web of interactions between the systems of the body. In each of these systems, imbalances can occur that contribute to disorders of weight regulation and metabolism.
A Functional Medicine doctor or heath care practitioner can help you figure out your own imbalances. In 2014 we started the Cleveland Clinic Center for Functional Medicine to help train doctors and health professionals and conduct the needed research in this field. I also have a practice with a wonderful group of Functional Medicine practitioners at The UltraWellness Center in Lenox, Massachusetts, who have helped thousands of people identify the root causes of their health issues. You can also find a certified practitioner through the Institute for Functional Medicine at www.functionalmedicine.org.
To help you sort through all the causes of weight gain and obesity I have created a special free e-book called Beyond Food: Other Causes of Obesity and Damaged Metabolism. You can download it at www.eatfatgetthin.com. There is also a free companion guide on testing and treatment, How to Work with Your Doctor to Get What You Need, where I explain how to assess and test for these causes and how to address them yourself or in partnership with your health care provider. In Beyond Food, I address the eight major causes of weight-loss resistance and what to do about them:
Reason #1: Nutritional Imbalances: Over Fed and Under Nourished
Reason #2: Gut Microbiome Imbalances: Bad Bugs and Weight Gain
Reason #3: Inflammation and Immune Function: Fueling the Fires of Fat Storage
Reason #4: Environmental Toxins: Poisoning Your Metabolism
Reason #5: Trouble with Your Energy Producing System (Your Metabolism)
Reason #6: Bad Communication: Fixing the Body’s Hormone Messengers
Reason #7: Is It My Genes that Prevent Me from Fitting in My Jeans?
Reason #8: “Catching Obesity”: The Role of Our Social Networks in Weight and Health
4
The Skinny on Fats
Fat is a complicated topic that inspires much debate among scientists and nutrition experts, but there’s one thing everyone can agree on: There is no such thing as simply “fat.” There are many different kinds of fats: some good, some good or bad, depending on certain factors, and some downright evil.
Foods often contain a wide variety of fats. For example, butter contains saturated fat, omega-3 fats, omega-6 fats, and monounsaturated fats. Some fatty foods such as nuts also contain protein and/or carbohydrates, which influence the effects of different fats on your body. Saturated fat, for instance, is bad when eaten with carbohydrates, but when eaten alone, not so much. See what I mean when I say it’s easy to be confused about fat?
Because everyone looks at just part of the story, very smart scientists can have completely opposing views on fat. Some say omega-6 vegetable oils are healthy and others suggest they are lethal. Some promote the benefits of saturated fats, while still others declare their dangers. There is a way to think through these contradictory views.
There is a new framework for thinking about human biology. It tells a holistic story of how everything is interconnected. So much of our nutrition research is made up of population studies that suggest linkages but don’t prove anything. For example, I could design a study to see if sex led to babies, but if I included only couples over fifty years old, I would conclude that sex does not result in babies. Silly, yes, but a lot of our research is done that way. Having an overarching theory allows us to make sense of the data. So what is that theory?
In systems biology, the dynamic real-time connections and interactions between environment, diet, and genetics can be mapped. The practical application of this approach is Functional Medicine. At its core it addresses the root causes of imbalances that drive disease—imbalances that result from the interaction of diet, environment, and genes. This is personalized medicine, medicine that understands we are all genetically and biochemically unique but are also hugely adaptable and as a species have thrived in diverse habitats a
nd environments, on widely different diets. In Chapter 10 I will review what I have come to understand as the foundational principles of an optimal human diet, which can vary greatly from culture to culture and be adapted to different preferences but is guided by a basic theoretical framework of what makes sense from an evolutionary and historical perspective.
Science is discovering the multidimensional role of food in health. Food is not just calories; it is information that instructs your minute-to-minute functions, which control all aspects of your health and disease risks. We have co-evolved with the food in our environment and use it to regulate every single bodily process, including our gene expression, inflammation, oxidative stress (damage from oxygen, like when an apple turns brown or a car rusts—think of it like rusting on the inside), hormonal function, immune function, gut flora balance, detoxification, metabolism, and much, much more. Insights from our historical diet can help guide us in what range of foods we might do well on.
While Eat Fat, Get Thin is about fat, what it is, what types we should eat, and how much we should eat, there are wide differences in diets in different populations. For example, the Japanese consume 15 percent of calories as fat, the Mediterranean cultures consume 40 percent of calories as fat, and the Pacific Islanders and the Masai warriors consume mostly saturated fats. Yet none of these populations have the high rates of modern civilization diseases such as obesity, heart disease, diabetes, cancer, and dementia that we have in America.