There are lots of things we want to do in life. Climb a mountain, write a song, watch our grandchildren grow up. But guess what? We can’t do any of those things if we don’t have our health.
Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. And I’m here to bring you evidence-based research that takes the mystery out of the best way to live a healthier, longer life.
Today on the show, Part 1 of my Keto Diet Series. “Keto” has been one of the most searched keywords on nutritionfacts.org for months. And today we’re going to find out why. Keto is short for ketogenic which describes a low carb high fat diet. But is it good for you? Does it work? In our first story, we explore the clinical uses of ketogenic diets for epilepsy and cancer. What does the science say?
Blood sugar, also known as blood glucose, is the universal go-to fuel for the cells throughout our bodies. Our brain burns through a quarter-pound of sugar a day, its “preferred metabolic fuel.” Our body can break down proteins and make glucose from scratch, but most comes from our diet in the form of sugars and starches. If we stop eating carbohydrates, or stop eating altogether, most of our cells switch over to burning fat. But fat has difficulty getting through the blood-brain barrier. But our brain has this constant massive need for fuel, one organ accounting for up to half of our energy needs. Without it, the lights go out…permanently.
To make that much sugar from scratch, our body would need to break down about a half-pound of protein a day. That means we’d cannibalize ourselves to death within two weeks. But people can fast for months. The answer to the puzzle was discovered in 1967. Harvard researchers famously stuck catheters into the brains of obese subjects who had been fasting for over a month, and discovered that ketones had replaced glucose as the preferred fuel for the brain. Your liver can turn fat into ketones, which can then breach the blood-brain barrier and sustain your brain if you’re not getting enough carbohydrates. Switching fuels has such an effect on brain activity that it has been used to treat epilepsy since antiquity.
The prescription of fasting for the treatment of epileptic seizures dates back to Hippocrates. In the Bible, Jesus seems to have concurred. To this day, it’s unclear why switching from blood sugar to ketones as a primary fuel source has such a dampening effect on brain overactivity. How long can you fast, though? To prolong the fasting therapy, in 1921 a distinguished physician scientist at the Mayo Clinic suggested trying what he called a “ketogenic diet,” a high-fat diet designed to be so deficient in carbohydrates it could effectively mimic the fasting state. “Remarkable improvement” was noted the first time it was put to the test—efficacy that was later confirmed in randomized, controlled trials. Ketogenic diets started to fall out of favor in 1938 with the discovery of the anti-seizure drug that would become known as Dilantin, but ketogenic diets are still in use today as a third- or fourth-line treatment for drug-refractory epilepsy in children.
Oddly, the success of ketogenic diets against pediatric epilepsy seems to get conflated by “keto diet” proponents into suggesting a ketogenic diet is beneficial for everyone. But you know what else sometimes works for intractable epilepsy? Brain surgery. But I don’t hear people at the gym clamoring to get their skulls sawed open.
Since when do medical therapies translate into healthy lifestyle choices? Scrambling brain activity with electroshock therapy can be helpful in some cases of major depression, so what…pass the electrodes? Ketogenic diets are also being tested to see if they can slow the growth of certain brain tumors. Even if it works, you know what else can help slow cancer growth? Chemotherapy. So why go keto when you can just go chemo?
Promoters of ketogenic diets for cancer, paid for by so-called “ketone technology” companies that will send you salted caramel bone broth powder for a hundred bucks a pound. Or companies that market ketogenic meals report “extraordinary anecdotal responses” in some cancer patients, but more concrete evidence is simply lacking. Even the theoretical underpinnings may be questionable. A common refrain is that “cancer feeds on sugar.” But all cells feed on sugar. Advocating ketogenic diets for cancer is like saying Hitler breathed air, so let’s boycott oxygen.
Cancer can feed on ketones, too. Ketones have been found to fuel human breast cancer growth, and drive metastases in an experimental model more than doubling tumor growth. Some have even speculated that may be why breast cancer often metastasizes to the liver, the main site of ketone production. If you drip ketones on breast cancer cells in a petri dish directly, the genes that get turned on and off make for a much more aggressive cancer, associated with a significantly lower five-year survival in breast cancer patients. Researchers are even considering designing ketone-blocking drugs to prevent further cancer growth by halting ketone production.
And think about what eating a ketogenic diet might entail. High animal fat intake may increase the mortality risk among breast cancer survivors, and potentially play a role in its development in the first place through oxidative stress, hormone disruption, or inflammation.
Men, too: “a strong association has also been found between saturated fat intake and prostate cancer progression.” Those in the top third of consumption of these kinds of fat-rich animal foods appeared to triple their risk of dying from prostate cancer. Not necessarily fat in general. No difference in breast cancer death rates based on total fat intake, but saturated fat intake may negatively impact breast cancer survival, a 50 percent increased risk of dying from breast cancer. There’s a reason the official American Cancer Society and American Society of Clinical Oncology Breast Cancer Survivorship Care Guidelines recommend a dietary pattern for breast cancer patients that’s essentially the opposite of a ketogenic diet: “high in vegetables, fruits, whole grains, and legumes, meaning beans, split peas, chickpeas and lentils, and low in saturated fats.”
So far, not a single clinical study has shown “a measurable benefit from a ketogenic diet for any human cancer.” There are currently at least a dozen trials underway, however, and the hope is that at least some cancer types will respond. Still, even then that wouldn’t serve as a basis for recommending ketogenic diets for the general population any more than recommending everyone go out and get radiation, surgery, and chemo for kicks.
In our next story, we ask do low-carb and ketogenic diets have a metabolic advantage for weight loss? Let’s find out.
When you don’t eat enough carbohydrates, you force your body to burn more fat. “However, this rise in fat burning is often misconstrued as a greater rate of net fat mass reduction on the body.” But that ignores the fact that on a ketogenic diet your fat intake shoots up as well. The question is what happens to your overall body fat balance. You can’t empty a tub by widening the drain if you’re cranking up the faucet at the same time. Low-carb advocates had a theory, though: the so-called “carbohydrate–insulin model of obesity.”
Proponents of low-carb diets, whether a ketogenic diet or a more relaxed form of carbohydrate restriction, suggested that the decreased insulin secretion would lead to less fat storage. And so, even if you were eating more fat, less of it would stick to your frame. So, we’d be burning more and storing less, the perfect combination for fat loss or so the theory went. To their credit, instead of just speculating about it, they decided to put it to the test.
Gary Taubes formed the Nutrition Science Initiative to sponsor research to validate the carbohydrate–insulin model. He’s the journalist who wrote the controversial 2002 New York Times Magazine piece, “What if It’s All Been a Big Fat Lie?”, which attempted to turn nutrition dogma on its head by arguing in favor of the Atkins diet, with its bunless bacon cheeseburgers based on the carbohydrate–insulin model. (Much of Nina Teicholz’s book The Big Fat Surprise is simply recycled from Taubes’s earlier work).
In response, some of the very researchers Taubes cited to support his thesis accused him of twisting their words. “The article was incredibly misleading,” one said. “I was horrified.” “He took this weird little idea and blew it up, and people believed him,” said another. “What a disaster.” It doesn’t matter what people say, though. All that matters is the science.
Taubes attracted $40 million in committed funding for his Nutrition Science Initiative to prove to the world you could lose more body fat on a ketogenic diet. They contracted noted NIH researcher Kevin Hall to perform the study. Seventeen overweight men were effectively locked in what’s called a metabolic ward for two months to allow researchers total control over their diets. For the first month, they were placed on a typical high-carbohydrate diet (50 percent carbohydrate; 35 percent fat; 15 percent protein), and then they were switched to a low-carb ketogenic diet (only 5 percent of calories from carbohydrate; 80 percent fat) for the second month. Both diets had the same number of daily calories. So, if a calorie is a calorie when it comes to weight loss, then there should be no difference in body fat loss on the regular diet versus the ketogenic diet. If Taubes was right, though, if fat calories were somehow less fattening, then body fat loss would become accelerated. What happened instead, in the very study funded by the Nutrition Science Initiative, was that “body fat loss slowed” upon switching to the ketogenic diet.
Wait, why do people think the keto diet works, if it’s actually slowing fat loss? Well, if you just looked at the readings on their bathroom scales, the ketogenic diet would seem like a smashing success. They went from losing less than a pound a week on the regular diet in the two weeks before they switched to losing three and a half pounds within seven days after the switch to the ketogenic diet. But what was happening inside their bodies told a totally different story. Their rate of body fat loss was slowed by more than half. So, most of what they were losing was just water weight. (The reason they started burning less fat on a ketogenic diet was presumed to be because without the preferred fuel, carbohydrates, their bodies started burning more of its own protein.)
And that’s exactly what happened. Switching to a ketogenic diet made them lose less fat mass and more fat-free mass; they lost more lean mass. That may help explain why the leg muscles of CrossFit trainees placed on a ketogenic diet may shrink as much as 8 percent. The vastus lateralis is your biggest quads muscle in your leg. Shrunk in thickness by 8 percent on a ketogenic diet.
Yes, the study subjects started burning more fat on the ketogenic diet, but they were also eating so much more fat on the ketogenic diet that they ended up retaining more fat in their body, despite the lower insulin levels. This is “diametrically opposite” to what the keto crowd predicted, and this from the guy they paid to support their theory. In science-speak, “the carbohydrate–insulin model failed experimental interrogation.”
In light of this “experimental falsification” of the low-carb theory, the Nutrition Science Initiative effectively collapsed, but based on their tax returns, not before Taubes and his co-founder personally pocketed millions of dollars in compensation.
In our final story today, we explore Ketogenic diets and the $33-billion diet gimmick.
The carbohydrate-insulin model of obesity, the underlying theory that ketogenic diets have some sort of metabolic advantage, has been experimentally falsified. The keto diet’s proponents’ own studies showed the exact opposite: ketogenic diets actually put you at a metabolic disadvantage and slow the loss of body fat. How much does fat loss slow down on a low-carb diet?
If you cut about 800 calories a day of carbohydrates from your diet, you lose 53 grams of body fat a day, but if you cut the same number of fat calories, you lose 89 grams a day. Same number of calories, but nine pats of butter worth of extra fat melting off your body every day on a low-fat diet, compared to a low-carb diet. Same number of calories, but about 80 percent more fat loss when you cut down on fat instead of carbs. Cut 800 calories from your diet by cutting carbs, and you do lose body fat. But cut out the same number of calories by cutting fat, and you lose even more body fat—80 percent more body fat lost. The title of the study speaks for itself: “Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity.”
But just looking at the bathroom scale, though, would mislead you into thinking the opposite. After six days on the low-carb diet, study subjects lost four pounds. On the low-fat diet, they lost less than three. So, step on the scale and it looks like the low-carb diet wins, hands down. So, you can see why low-carb diets are so popular.
But what was happening inside their bodies tells the real story. The low-carb group was losing mostly lean mass, water and protein. This loss of water weight helps explain why low-carb diets have been “such ‘cash cows’ for publishers” over the last 150 years. That’s their secret. As one weight loss expert noted, “Rapid water loss is the $33-billion diet gimmick.”
When you eat carbohydrates, your body bulks your muscles up with glycogen for quick energy. Eat a high-carbohydrate diet for three days, and you may add about three pounds of muscle mass onto your arms and legs. Those glycogen stores drain away on a low-carb diet, and pull water out with it. (And, the ketones also need to be flushed out of the kidneys, pulling out even more water.) On the scale, that can manifest as four more pounds coming off within 10 days, but that all can be accounted for in water loss.
The bottom line: keto diets just don’t hold water.
But the thrill of seeing the pounds come off so quickly on the scale keeps many coming back. When the diet fails, the dieters often blame themselves. But the intoxication of that initial rapid weight loss may tempt them back, like getting drunk again after forgetting how terrible the last hangover was. This has been dubbed “the false hope syndrome.” The diet industry thrives off of “repeat customers,” something low-carb diets were built for, given that rapid initial water loss.
But what we care about is body fat. In six days, the low-fat diet extracted a total of 80 percent more fat from the body than the low-carb diet. And it’s not just one study. If you look at all the controlled feeding trials where researchers compared low-carb diets to low-fat diets, swapping the same number of carb calories for fat calories or vice versa. If a calorie is just a calorie, then all the studies should have crossed this zero line in the middle, and indeed, six did. One study showed more fat loss on a low-carb diet, but every other study favored the low-fat diet: more loss of body fat eating the same number of calories. Put all the studies together and we’re talking 16 grams more daily body fat loss on the low-fat diets. That’s four more pats of butter melting off your body on a daily basis. Less fat in the mouth means less fat on the hips, even taking in the same number of calories.
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Thanks for listening to Nutrition Facts. I’m your host, Dr. Michael Greger.