Over the last three decades, in an attempt to make Americans and their diets healthier, nutrition experts have drifted more and more toward recommending eating less fat. In 2010, for example, the U.S. Department of Agriculture’s Dietary Guidelines recommended that adults consume 45 to 65 percent of calories in the form of carbohydrates, with only 10 to 25 percent and 20 to 35 percent coming from protein and fat, respectively. And yet, after all those years, we’re fatter — and sicker — than ever. In fact, faced with a growing population of obese and metabolically damaged people, it’s hard not to argue that this approach has actually made things worse. How can that be?
You can almost certainly blame carbohydrates — particularly sugar. One of the three macronutrients (protein and fat are the other two), carbs are the easiest source of energy for the body, and in fact, glucose, one of the simplest of all carbs, is what the brain preferentially uses to fuel itself.
Carbohydrates are classified as simple or complex depending on their chemical structure and how quickly the sugar is digested and absorbed. Simple carbohydrates — such as those found in fruit, milk/dairy, candy and table sugar — are made up of smaller sugar molecules and are easily digested, whereas complex carbohydrates, like more slowly digested starches and fibers, are made up of longer chains of sugar molecules.
But here’s the thing that nutritionists didn’t consider back when they started recommending that everyone watch how much fat they were eating. When you reduce intake of one nutrient, you must replace it with another one. And as people started eating less fat, they tended to eat more carbohydrates — and we’re not talking fruit and other fibrous carbs; instead, they ate more bread and pasta and processed foods that had the words “low-fat” blaring right there on the label. Just like with diets, when companies remove a nutrient from their processed foods, they have to replace it with another one to make sure that the resulting product still tastes good. So when fat comes out, carbs go in. (You can see this for yourself: Go to the supermarket and compare carb content in any regular salad dressing and a low-fat version of the same exact dressing. Or pick any other type of food. Low-fat foods almost always contain more carbs.)
There is now a significant body of research that indicates that when you remove fat from the diet and replace it with carbs, the result is not, as might be expected, a reduction in cholesterol, triglycerides and body fat but rather an increase in risk of negative health outcomes, including cardiovascular disease and obesity. And for that, you can blame (among other things) insulin.
Does your colleague fall asleep at his desk after lunch? What about that chick who becomes a monster when she’s unable to eat every couple of hours? Welcome to carbohydrate dependency.
As anyone who has ever tried a low-carb diet knows, one of the biggest challenges when attempting to curb or even just control carbohydrate intake is carbs’ potency. Eating carbohydrates compels repeated eating of carbohydrates. Carbohydrate-filled foods are convenient, especially the poorer-quality options, and the sugars they deliver have been proven addictive.
People who depend on carbohydrates as their major fuel source — let’s call them “sugar burners” — typically fall victim to the whims of the storage hormone insulin. Sugar burners display symptoms that include sugar cravings, mood swings and the predictable energy roller coaster that most notably crashes around 2 to 3 in the afternoon.
Sugar burners also might be toting around a bit more body fat than they’d like. Research shows that specific kinds of calories, rather than simply too many calories, might be to blame for making people fat. Calories from simple, refined carbohydrates (especially sugar) stimulate the release of the building and storage hormone insulin. If you’re eating carbs every few hours, insulin will always be around and will keep your body in fat-storage mode. Envision a scenario in which fat is repeatedly stuffed into cells without being released for burning. When this happens, the body runs low on fuel and the brain gets confused, assumes you’re starving and makes you feel hungry. As a result, you crave more carbohydrates and repeat the cycle, which is why sugar burners eat almost constantly throughout the day.
On the flip side, a person who restricts his or her carbohydrate intake and runs mainly on fat — a “fat burner” — experiences low insulin levels and has fat cells with open doors that allow fat to escape and be burned for energy. Fat burners don’t suffer from constant hunger. As described by Michael Eades, M.D., co-author of Protein Power and The 30-Day Low-Carb Diet Solution, even if your dietary intake of fat meets all your body’s energy needs, your body will simply use these fat calories for energy instead of tapping into your fat cells. This translates to weight maintenance and the phenomenon that when insulin is low, fat pretty much can’t get into your fat cells. Said another way: Even if your caloric intake goes up, if you remain carb restricted, you won’t store more fat in your fat cells and you will maintain your weight.
Unlike with fats and proteins, which you must consume because the body is not capable of producing them, carbohydrates are a nonessential macronutrient; the body can generate any glucose it needs all by itself, through a process called gluconeogenesis. However, be warned that there is an unpleasant adjustment period for sugar burners to convert to fat burners. It can take anywhere from 24 hours to two or three weeks for the body to complete this transition, and while you’re in the thick of it, you’ll generally experience fatigue, mental cloudiness and an overwhelming craving for carbohydrates. This happens because the body is transitioning fuel types; it has to sort through all the tools hidden in its attic to find the ones needed for burning fat. Once the tool kit is replaced, you start thriving on your new low-carbohydrate, higher-fat diet, readily using fat as your primary source of energy.
We can hear the shouts of dissent now: Carbs have been thought critical for highly active athletes and particularly for endurance athletes. And yes, it’s true. Carbs, being the fast and easy energy source they are, have a long tradition of being consumed in vast quantities before races and other competitions. But recently there have been some interesting shifts in fat and carbohydrate recommendations; more endurance athletes are turning to fat for fuel, both in training and competition.
Using self-experimentation, elite triathlete Ben Greenfield has provided one of the most popular and well-documented examples of this. Stephen Phinney, M.D., Ph.D., an expert in low-carb lifestyles, has also shown the value of becoming fat adapted. In one of his studies, cyclists followed a carbohydrate-restricted diet for four weeks, after which their performance was just as stellar without carbohydrates because ketones — an alternative fuel source formed when fat is burned — precluded their need for glucose. Phinney and colleagues have recently calculated that a fat burner oxidizing fat at 1.5 grams per minute would cover his energy cost during an Ironman triathlon without needing to eat any food during the race. On the other hand, sugar burners would need to ingest 90 to 105 grams of carbs per hour during prolonged exercise to maintain performance. And a recent study done in mice illuminated other benefits of low-carb diets — it reported that carbohydrate restriction also can lead to reduced oxidative stress, an effect that could theoretically improve postworkout recovery times.
One way to think about the different roles of fat and carbohydrates in training is to take a page from Nora Gedgaudas, CNS, CNT, author of Primal Body, Primal Mind: Beyond the Paleo Diet for Total Health and a Longer Life, and liken human metabolism to a fire. In this context, carbohydrates are the kindling, sticks, twigs and paper, while fat is the log. You can get a fire going quickly using the former, but without logs, you’d find yourself slaving over it all day just to keep it going. On the other hand, it takes time to get a log burning, but once it’s going, all you have to do is add to it every several hours to keep up the momentum. For prolonged endurance performance, athletes who train their bodies to use fat as the predominant fuel get more bang for their buck because that fuel tank — the total amount of stored body fat — is more than 10 times larger than the carbohydrate tank — the glycogen stored in your muscles and liver. Athletes who fuel with carbohydrates require a lot of them and often, while those who have become fat adapted can perform for long periods before needing to refuel.
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But if you’re fully into the analogy, you’ll have realized that most fires don’t consist of solely sticks and twigs or logs; they contain both. Apply this to sports and it’s reasonable to conclude that finding the perfect combination of fat and carb intake is what matters most. Just as throwing sticks or paper into a burning fire will boost the flames, an athlete who is fat adapted can thrive by strategically adding carbohydrates to his or her diet at the right times. While fat is appropriately becoming the focus for many endurance athletes, carbohydrates should still be recognized as a fast fuel source, optimal for explosive activities like interval hill sprints and one-rep-max lifts. Metabolic-conditioning workouts are another example for which carbohydrates are beneficial and even necessary.
Some Good News
As nutrition science changes its mind about the true benefits of carbs, there is one area in which the controversial nutrient is showing itself to be valuable. Carbohydrates have been gaining appreciation for their role in gut health, a sexy topic of ongoing rigorous study. It seems that even though the fibers found in fruits, vegetables, starchy plants, nuts, seeds and legumes are poorly absorbed by humans, they do provide a gourmet food source for intestinal bacteria. Unfortunately, many of these fiber-rich foods are also rich in carbohydrates and would be eliminated on very low carbohydrate diets. Because bacteria feed on carbohydrates, and in doing so produce beneficial byproducts (e.g., short-chain fatty acids) for our bodies to use, this can have overall adverse effects on long-term health.
For his patients who follow a ketogenic or very low carbohydrate diet for medical purposes, Chris Kresser, MS, L.Ac., author of Your Personal Paleo Code, recommends regular consumption of non-digestible fermentable fibers (e.g., resistant starch), which don’t count toward daily carbohydrate intake because humans can’t digest them. Because resistant starch can’t be broken down by human intestines, it travels intact to the colon, where all the bacterial beasties go to town, gobbling it up and producing the above-mentioned short-chain fatty acids for your benefit. The richest sources of the starch are raw potatoes, plantains and unripe bananas. It’s also plentiful in potatoes, rice and legumes that have been cooked and then cooled.
Grooming your beneficial gut bacteria is important because it’s believed that gut microbiota also can modulate metabolism. This would explain why the population of gut bacteria in obese people often differs from that in healthy people. Recent research suggests that consuming dietary fiber and carbohydrates that bacteria can eat (like, for example, resistant starch) improves overall gut microbiota. A study of 38 obese and 11 overweight individuals published in 2013 in Nature reported that those with a less rich and diverse gut bacterial pool showed greater signs of dysregulated metabolism and inflammation. But interestingly, the gut microbiota and clinical measures were improved following a change in diet.
Another reason not to eliminate carbs entirely: Carbohydrate intake also can impact hormones — namely those produced by the thyroid and adrenal glands. Some people who attempt low-carbohydrate diets face hormone-related symptoms like fatigue, burnout and restlessness. When it comes to thyroid hormone, insulin is needed for conversion of the inactive form (T4) to the active form (T3). This presents a dilemma. On one hand, low levels of insulin are a key benefit of low-carbohydrate diets, but on the other hand, insufficient insulin could lead to hypothyroidism (inadequate levels of thyroid hormone).
Adrenal fatigue is another condition that often warrants increased carbohydrate consumption. Dysregulation of the stress hormone cortisol, which tends to increase with low-carbohydrate dieting, is a hallmark of adrenal fatigue. This suggests that the body perceives carbohydrate restriction as stressful and that adding healthy fruits and tubers back into the diet might be a good idea. So regardless of whether you’re facing deadlines at work, are having nightly fights with your partner or are restricting carbohydrates, the resulting stress is likely to adversely affect cortisol levels. Changes in cortisol regulation often manifest as poor sleep quality, which is also a common consequence of chronic low-carbohydrate dieting. If you’re going through a stressful time in your life and/or are having trouble sleeping, it’s the wrong time to add carbohydrate restriction to the mix. Instead, do yourself a favor and enjoy your steak — and sweet potatoes, too.
Despite the potential benefits of carbohydrate restriction, the bottom line is, it’s a lifestyle that’s difficult to maintain in the real world. But if you’re curious about what a low-carbohydrate regimen could do for you, do some research and get dirty in the kitchen. Rather than go straight to the grocery store to purchase processed low-carbohydrate foods, discover the variety of low-carbohydrate, nutrient-dense, real food that you can prepare in your own kitchen. The Atkins diet might be one option, but it demands nothing of food quality nor will it engage your lifestyle. The safest approach and one you’re most likely to follow is a primal-based, whole-food diet that requires your active participation — cooking pasture-raised eggs and rib-eye steaks rather than scarfing down protein bars.