“Terrible thing, to live in fear.”

Morgan Freeman spoke these words in one of the greatest movies ever (based on a novella by one of the greatest horror authors ever). Another line of Freeman’s from that movie is “Get busy living, or get busy dying.”

If you’re a fan of busy living, you must not live in fear of carbohydrates.

Fear of carbs and lauding of fat came about due to misinformation. In the 1970s, nutrition guidelines recommended we cut fat intake, and obesity exploded. So, cutting fat = bad, right?

Wrong. Because people never cut fat. A 2013 analysis published in The American Journal of Clinical Nutrition found that fat intake has stayed very stable across the decades. In other words, we never paid any attention to the recommendations. Instead, we just ate a lot more. A 2009 study published in The American Journal of Clinical Nutrition determined that, since the 70s, adults increased average consumption by 500 calories per day, and children began eating 350 more calories per day.

Alas, “Eat less” doesn’t sell diet books, but “Eat bacon” does.

When people saw the money an Atkins-like approach could generate, it spun off in every conceivable direction, including caveman diets, butter in coffee, and the cult-like vilification of sugar. And for some people such diets do work, not via any caloric-balance violating macronutrient ratios and not because of superior satiety, but due to the low rule complexity of avoiding carbs.

This demonization of carbs and lauding of eating fat has spread to the athletic sphere, with many promoting it as a superior source of fuel for exercise performance. And it is complete and utter male bovine droppings.

Think going very low carb / very high fat is the route to improved performance? You’re destined to lose to a better fueled athlete. The evidence that carbs are superior for performance is undeniable, and the concept of the “keto athlete” winning races is bogus. (Note: “keto” refers to a ketogenic diet that involves severe carbohydrate restriction of less than 50 grams per day, favoring high fat intake instead.)

And while I’m about to show how keto doesn’t fire you up for high performance, the diet itself is on fire right now. Look at what Google Trends reveals for the interest in the diet over the last five years.

And it’s a dangerous trend for anyone interest in improving performance. Let’s lay down the evidence.

Straws, Firehoses, and Race-Winning Moves
Even when training for a marathon, some speed-work is necessary. When I was training to qualify for the Boston Marathon I did speed work at least once and sometimes twice a week. This usually involved doing intervals of four minutes of going slow, followed by four minutes of balls out as fast as I could sustain.

But if you’re carb depleted, “as fast as you can sustain” is slower. The comparison of fuel sources is analogous to drag racing.

“Top Fuel” drag racers are the fastest accelerating racing vehicles in the world, but they don’t fuel up at the local 7-11. That’s because the gasoline you put in your Honda is like eating fat, and drag race fuel is like carbs.

It has to do with both burn rate and energy density. Gasoline has more available energy per liter than Top Fuel, just as fat has more energy than carbs (9 calories per gram vs. 4). More importantly, both gasoline and fat burn at a much slower rate than Top Fuel and carbohydrates do.

“The amount of energy the body can extract from carbs is much greater per unit of time than the energy it can extract from fat,” nutrition expert Alan Aragon, co-author of The Lean Muscle Diet, told me. “When carbs are oxidized, they yield two-to-five times more ATP (energy) than fat.”

Aragon explained that when using fat for fuel, “You can’t access that energy as quickly. With fat, you have a bigger pool of energy, but you can only drain it with a straw. With carbs, the pool is smaller but you can drain it with a firehose.”

At low and moderate intensities, this doesn’t matter much. If you’re always at cruising speed and the straw provides enough fuel, then that’s okay. But would you never want to go high-intensity? And I’m not just talking about aerobic activity. Any type of physical activity is going to be limited to moderate intensity if you eschew rather than chew carbohydrates. Forget being able to sprint worth a damn. And very low carb will have a negative effect on weight lifting performance as well (more on that later).

As I said, even marathon runners do some high-intensity work in training to improve their performance on race day. During long distance races, there will be times you need to push up a hill or do a finishing kick – so called “race-winning moves.”

If you’re not carbed up, you can’t win.

Fake Keto Athletes
Ultra-running is one of those sports the keto crowd says their diet is superior for, because it’s largely done at moderate intensity. And they hold up some of the best ultra-runners as being keto and therefore keto is awesome and you should do keto and everyone should do keto and carbs are evil and won’t someone think of the children.

Except those runners aren’t on ketogenic diets.

In 2014, Ultrarunning Magazine wrote a piece titled: “Zack Bitter: Fastest 100-Miler in U.S. History.” The piece lauds his ketogenic diet and reads like an advertorial for Vespa, a “keto-adaptation” supplement. In fact, Vespa has its own Zack Bitter page on their site, and Bitter promotes the company on his site, so I expect some money is changing hands.

The real contradiction comes from Zack’s own statements in the article and elsewhere: “I consume plenty of fresh vegetables and fruits … This diet is hardly depriving except that I am not having a ton of refined carbohydrates.” But he seems to be eating plenty of unrefined ones, especially at race time: “carbs are ‘strategically’ brought back (as at a race),” the article says. And on his website, Bitter wrote: “most of my carbohydrates are consumed during or around workouts.” At that same link, he spoke of eating potatoes and sweet potatoes.

Doesn’t sound very keto to me. And it’s not the only example.

This 2012 interview with Steve Phinney, co-author of The Art and Science of Low Carbohydrate Performance, is amusing in its delusion. The interview is about ultrarunner Tim Olson, who had recently won the Western States 100-miler. In the interview, Phinney speaks of Olson as an “openly professed low-carb runner.” Then Phinney says of Olson’s diet, “I wouldn’t tell you the details even if I knew because it’s confidential research information.”

So, Phinney makes grand statements about a low-carb athlete then says he doesn’t know what he eats? Except we do know what Olson eats, per his website: “I still use carbs, but mostly in the form of sweet potatoes and fruits. When I do eat carbs I use them strategically; I’ll eat sweet potatoes with lots of coconut oil the night before a race or long/intense run. I’ll have a green smoothie after a hard run with fruit and whey protein to replenish my glycogen storage.”

Again, what we have here is a supposed low-carb athlete consuming a bunch of carbs for training, recovery and for races. Because, you know, it’s the best fuel for doing so.

Sub-Optimal Performance
Ask fans of the L.A. Lakers what low carb does for athletics, says Alan Aragon. He pointed out how the team went low carb paleo at the recommendation of keto dieting advocate Dr. Cate Shanahan (Shanahan is a physician, not a registered dietitian – read my article here about why MDs are usually a terrible choice for dietary advice.) And guess what happened? The team tanked in the rankings. The season that followed the decision to go paleo was the worst in the 67 years of the franchise, with 61 losses and only 21 wins.

“But what about those living in the far north?” This question has been asked by many a keto advocate to justify their diet. The historical Inuit diet has been one of high fat and very little carbs, due to simple lack of availability of grains, fruits and vegetables in such a rugged climate. Susan Kleiner, PhD, RD, and author of Power Eating, puts this into context: “I don’t know how much sprinting the Inuit do,” she said. “They do heavy work, but not high-intensity running.” More importantly, she adds, “Were they the most efficient they could have been? If they had access to carbs for fuel would it not have been better for them? They survived, but was it optimal?”

Alan Aragon says you don’t have to have carbohydrates to survive, but adds, “There is a difference between surviving and thriving.”

Rob Skinner, Senior Sports Dietitian for Team USA, agrees that carbs help us thrive. He advises Olympic-level combat athletes, who sometimes go low carb to cut weight (low carb causes temporary water loss) to make their weight category. “Power and strength goes down,” he said. Skinner also lauded carbohydrates for their protein-sparing effect. “They let your protein be used for building muscle rather than for energy,” he said.

Demystifying “Keto Adaptation”
“How long does it take to ‘fat adapt’? Apparently, always one week longer than the study proving it sabotages endurance fitness.” I saw this sarcastic post on Facebook, written by 2:41 marathoner Matt Fitzgerald, author of The Endurance Diet.

What Matt is talking about is how many keto proponents say that every study of the performance effects of keto didn’t give the study subjects long enough to adapt their bodies to using fat as fuel instead of being a nasty ol’ “sugar burner.”

“The most measurable feature of keto adaptation is that your body increase fat oxidization,” said Aragon. “You can measure this via respiratory exchange ratio. The data shows it plateaus within the first week of going on keto. The idea that you need to go for several months to really fat adapt is bullshit.”

Aragon went on to explain that just because your body becomes better at burning fat doesn’t mean this enhances performance. “You decrease your ability to burn carbs,” he said. “You become ‘carb impaired’ because pyruvate dehydrogenase, the enzyme that allows your body to break down glycogen and access to glucose to extract ATP, decreases. This is exactly why people who keto adapt have repeatedly had impaired sprinting performance.”

It’s also worth noting that Aragon says, “You’re not burning more body fat, per se. The increase in fat oxidation is a direct result of an increased ingestion of dietary fat. Eat more fat, burn more fat. But your love handles are not decreasing. No difference in body fat reduction has been seen, as long as you equate protein and total calories.”

A Closer Look at the Research
In 1983, there was a study of how chronic ketosis affected cycling performance, and they found it didn’t make any difference to consuming adequate carbohydrates.

There is a gigantic, all caps “BUT” that goes along with that.

Conducted by Dr. Steve Phinney, who was mentioned earlier, the study only looked at five cyclists, and more importantly, the participants were far below maximal effort (65% of VO2max). That’s a pretty easy ride, and therefore the fuel being used to feed it can be achieved via a straw. The firehose isn’t needed.

What’s more, two decades later, Phinney wrote of his 1983 study in Nutrition and Metabolism in 2004 that, “sprint capability … remained constrained during the period of carbohydrate restriction.”

This is keto proponent Steve Phinney coming right out and saying if you want to go above a moderate pace, keto sucks. But even for moderate intensity it may not be that great, the results of a recent study reveal.

Last year 21 elite race walkers, many of whom were headed to Rio to compete in the 2016 Olympic Games, were placed on one of three strictly controlled diets. Just published in the Journal of Physiology, the study had two high carb groups (60-65% of calories from carbohydrates, where the only difference between the two was how carbohydrate ingestion was timed) and ketogenic (less than 50 grams of carbs, with 75-80% of calories coming from fat).

As a reminder, these guys are race walkers. It’s more than sprinting performance being impaired.

As expected, the high fat, low carb group saw dramatic increase in using fat for fuel (because that’s what they were eating). But the study also found that efficiency went down, meaning they had a much higher oxygen usage to sustain pace. That’s bad.

The performance results are more telling. A 10K race walk was conducted at the beginning and end of the trial. Following the three-week training and four-week diet intervention, the two high carbohydrate groups improved their times by 6.6% and 5.3%. The keto group, however, despite the intense training, saw a 1.6% reduction in performance (not enough to be considered a statistically significant performance decrease, but certainly no improvement).

The Weight of the Evidence
Susan Kleiner shared with me a screen shot of research examining ketogenic diet and athletic performance. Seventeen of the studies showed a performance decrease, and only two showed a performance increase, but both of those “performance increase” studies came with caveats (intensity was only moderate / carbohydrate loading for performance was possible / no muscle biopsies to prove ketogenic state).

To add to this, here is a sample of studies showing the benefits of carbohydrates for performance:

  • Journal of Strength and Conditioning Research, 2003: “it may be advisable for athletes who are performing high-volume resistance training to ingest carbohydrate supplements before, during, and immediately after resistance training.”
  • International Journal of Sport Nutrition and Exercise Metabolism, 2006: Study compared high protein vs. high carb on cycling performance and asserted that for high protein: “Performance was significantly impaired.”
  • Journal of Sports Sciences, 2011: “During sustained high-intensity sports lasting ~1 h, small amounts of carbohydrate, including even mouth-rinsing, enhance performance via central nervous system effects.”
  • Applied Physiology, Nutrition and Metabolism, 2013: “a low-CHO (carbohydrate) diet reduces both performance and total aerobic energy provision during supramaximal (very high intensity) exercise.”
  • Sports Medicine, 2013: “small amounts of carbohydrate ingestion during exercise may also enhance the performance of shorter (45-60 min), more intense (>75 % peak oxygen uptake; VO(₂peak)) exercise bouts, despite the fact that endogenous carbohydrate stores are unlikely to be limiting. The mechanism(s) responsible for such ergogenic properties of carbohydrate ingestion during short, more intense exercise bouts has been suggested to reside in the central nervous system.” This means that simply tasting carbs is enough to get your brain to open the already existing energy stores in the bloodstream, enhancing performance.

How Much Carbohydrate Do YOU Need to Perform?
Carbohydrate intake is based on activity level. More activity = more carbs.

Even if you’re not that active, Kleiner cautions going too low on carbohydrate intake, “In most people, a diet of less than 40% carbohydrates is literally depressing,” she said. “If you have a tendency towards depression, a low carb diet raises your risk.”

Kleiner further clarified: “No one is advocating that you add a sugar bowl to your diet. We’re talking about whole foods and timing carbohydrate intake around exercise.” This means don’t save all your carbs for before bedtime. Eat healthy carbohydrates, mostly around training.

I asked her what she thought about the guy who isn’t into aerobic exercise and Kleiner replied, “There isn’t much difference in fueling strategy between a guy who only lifts weights and a guy who runs 10Ks,” she said. The lifter needs carbs just as much because maximizing muscle hypertrophy requires some high-intensity work.

The sport nutrition guidelines aren’t based in percentages, but rather in grams per kilogram of bodyweight. Alan Aragon explained that for someone interested in general fitness, the recommendation is 3-5 grams of carbohydrates per kilo of body weight. So, if a recreational athlete weighs in at 80 kilos (176 lbs), he’s going to want to consume between 240 and 400 grams of carbs each day.

If you want to break that down further, say he’s taking in 2,500 calories per day. The carb recommendation works out to between 960 and 1,600 calories. That’s a percentage range of a minimum of 38.4% from carbs, up to 64% of calories from carbs.

For more activity, the carb requirement goes up. Competitive sport athletes need up to 5-8 grams of carbohydrates per kilo, and people competing in ultra-distance should consume up to 10 or even 12 grams of carbohydrates per kilo of body weight. Note that the percentage of carbs in the diet won’t be a whole lot higher than the recreational athlete, because their total calorie intake is going way up commensurate with their very high level of activity.

Rob Skinner does warn about high carbohydrate intake, however: “When we give massive amounts of carbs to sedentary people, we see issues.” For the inactive, cutting back on carbs can be wise. However, he added that, “Adding a stick of butter to your coffee doesn’t seem like a smart thing to do. I’m not saying you can’t have saturated fat, but you don’t want to try to get more of it.”

I don’t expect many anti-carb cultists will be convinced by the evidence in this article, as they’re too firmly entrenched in their dietary beliefs, engaging in motivated reasoning to rationalize their eating strategies. But now you know that you can poke fun at their dietary delusions then run away, because they’ll never be able to catch you.


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James S. Fell, MBA, writes for the Los Angeles Times, Chicago Tribune, Women’s Health, Men’s Health, AskMen, the Guardian, TIME Magazine and many other fine publications. His first book was published by Random House Canada in 2014. He is currently working on his next book, which is about life-changing moments.