Dr. David Ludwig on high-carb vs low-carb vs slow-carb diets
I came across this short talk Dr. David Ludwig gave on some of his research on the difference between high-carb, low-carb, and slow-carb diets. The presentation is a great summary of the calories-in/calories-out way of thinking of dieting versus the alternative hypothesis, which is that carbs drive insulin, and insulin drives fat storage. Dr. Ludwig discusses some of his own research on the many physiological changes that take place when substituting carbs that absorb more slowly for those that rapidly absorb. I learned a few things from this lecture, so I figured it was worthwhile to pass along. It is very much worth the short time it takes to watch. I’ve put up the show notes and my comments and summary below.
0:42 First law of thermodynamics and calories in vs calories out (CICO), i.e., the conventional understanding of obesity
2:09 The simple (conventional) solution to obesity is to eat less and move more.
3:07 If the conventional solution to obesity is correct, then the low-fat diet will be your best friend.
4:06 But fat calories decreased as the obesity epidemic exploded.
4:35 Womens Health Initiative (WHI), the largest low-fat diet study ever done, or ever likely to be done, was an absolute bust. The deck was stacked in favor of the low-fat diet in that those on the low-fat diet got a ton of intensive individual counseling and guidance during periodic meetings with nutritionists whereas the control subjects were given written materials to study. Despite the extra attention given the subjects on the low-fat arm of the study, they didn’t do any better than those more or less left to themselves.
5:10 The Hawthorn Effect
5:35 Multiple meta-analyses show subjects on high-fat diets consistently lose weight better than those on low-fat diets. This raises the possibility that the mainstream’s “primary approach to nutrition, the low-fat diet, has caused major public health harm.”
6:28 NHANES shows that only one in six overweight people have ever lost more than 10 percent of their body weight and kept it off for over one year.
7:00 We have to ask, Why has the simple CICO system of weight loss been such an abject failure?
7:27 Answer: Body weight is controlled more by biology than will power over the long term.
8:35 Hunger is a primal biological signal that is very difficult to ignore. If you are able to ignore it or suppress it, your body fights back in other ways.
8:57 Nice discussion of what happens during overfeeding studies. Subjects gain weight, but lose interest in food and end up being as miserable as those on starvation diets. When the study is over, their weight drops back down to what it was at the start.
9:42 Results from these low-calorie and force feeding studies imply a body-weight set point that we defend. But if such a set point exists, why has it gone up year after year for the past 30-40 years? In the US, we’re defending a body weight that is 35 pounds higher than in was in the 1970s. Why? What can we do about it?
10:42 Begins a nice discussion of the alternative theory of obesity. If you’re unsure what the alternative theory is, this is a short incisive discussion that takes just a couple of minutes.
12:10 From the perspective of the alternative theory, eat less, move more is simply a symptomatic treatment, doomed to failure in the long run.
12:30 What causes the fat gain? Insulin. Insulin is the Miracle Grow for your fat cells, which is not the miracle you want happening in your body.
13:17 The glycemic index. As most of you know, I’m not a big fan of the glycemic index for a lot of different reasons, but, as we shall see as Dr. Ludwig’s talk continues, the more slowly absorbing carbs act more like low-carb foods and don’t create nearly the metabolic havoc that easily digestible carbs do.
14:10 Begins description of study on obese adolescents given one of three different meals for breakfast. One meal is instant oatmeal made of whole grains prepared in Dr. Ludwig’s lab. Steel cut oats made up the second meal. And the third meal was a vegetable omelette. The first two meals both contained the same amount of protein, fat and carbs and the same number of calories. The only difference was the variation in the speed of absorption of the carbs. The third meal had no almost no carbs, so it served as the control.
15:20 Insulin and glucose rises faster and higher after the instant oatmeal meal. Blood sugar crashes after the instant oatmeal meal. And the fatty acids (your real main fuel) are suppressed after the two oatmeal meals, but stay suppressed longer after the highly absorbable one, giving credence to the idea that the fat stays trapped in the fat cells.
16:33 Adrenaline (an emergency stress hormone) surged after the instant oatmeal meal.
17:10 After the breakfast meal, when all the subjects were given free access to food, those who had eaten the highly absorbable instant oatmeal ate 600kcal-700kcal more than the other subjects.
17:28 What happens in the brain when fatty acids and glucose fall while adrenaline rises? Let’s look at another study in which subjects got one of two milkshakes, one of which was sweetened with quickly digested corn syrup while the other was made with slowly digested, uncooked corn starch. Both shakes had the same number of calories, the same fat/protein content and the same sweetness. From a taste standpoint, they were identical.
18:20 Saw the same surge of blood sugar, insulin, and adrenaline, followed by a crash in blood sugar as before.
18:38 Brain scans showed the same areas lighting up as do so with cocaine, heroin, alcohol, tobacco, etc. Which gives rise to the notion that certain foods may trigger a process akin to addiction. Here is the part I found interesting and that I hadn’t really considered. The lighting up of the brain didn’t come because of taste, because both milkshakes tasted the same. The changes came via their biological effects.
19:32 “Palatability isn’t an inherent aspect of food.” I had never really thought of this or about this, but it’s true. After you’ve stuffed yourself with Thanksgiving dinner and are lying in a stupor, the stuffing that seemed so good when you ate it almost revolts you to even think about eating. Yet the stuffing is the same. It’s your perception of it that has changed based on your own physiology. “Palatability is an internal psychological response; it’s not something internal to food.”
20:45 Interesting rodent study. Two groups of rats went on two diets – one made of slowly digested carbs and one of quickly digested carbs – for 16 weeks (about ten rat years). The researchers fiddled with the caloric intake in an effort to keep the rats all weighing the same for the duration of the study. Interestingly, they had to restrict the caloric intake of the rats on the quickly digested carb diet in order to keep them at the same weight as their mates on the slowly digested carb diet. The metabolic rate of the rats eating the quickly digested carbs had slowed to the point that their caloric intake had to be restricted to prevent their becoming obese.
21:55 At the end of the study, the rats in both groups weighed the same, but the rats on the quickly digested carb diet sported 70 percent more body fat than the others. Remember, that’s on a lower number of calories, which can’t be explained by the CICO model of obesity. I know these are rodents and not humans, but this should be a cautionary tale about what happens when you eat a lot of easily digestible carbs.
23:00 A human study showed similar effects. Took 21 obese young adults and put them on a restricted diet till they lost 10-15 percent of their body weight, then put them on one of three diets: a low-fat, low-kcal diet; a low-carb, high-fat diet; or a Mediterranean diet.
Before the first weight loss diet, they were burning 3200 kcal/day. After they lost 10-15 percent of their body weight, when they went on the higher glycemic low-fat, low-kcal maintenance diet, their caloric intake had to be reduced by almost 400 kcal to maintain the lower weight. In contrast, when they maintained on the low-carb, high-fat diet, their calories had to be decreased a bit, but not nearly as much as those on the low-fat diet. The Mediterranean diet was kind of in the middle. It bears repeating: it took a reduction of 325 kcal below the caloric starting point on the low-carb, high-fat diet to maintain the lower weight. A huge difference.
24:45 We’ve all heard countless people say that it doesn’t matter what diet you go on, as long as you cut calories, you’ll lose weight. The composition of the diet doesn’t matter; you’ve just got to stick with it.
25:07 This notion comes from the POUNDS LOST study, which looked at 800 people (a lot for a weight loss study) studied for two years in two different academic centers. The subjects went on one of four different diets of varying compositions. Dietitians gave written instructions on how to carry out the diet and provided minimal counseling. At the end, all groups lost about the same amount of weight, confirming the notion that it doesn’t really matter what kind of diet you go on.
26:23 The above is a false conclusion. The study failed to achieve anywhere near its targeted nutrient differences.
27:18 When you look at the actual bio-measurements, they all look the same, so it’s pretty clear that they were all on more or less the same diet, so you would expect the same outcome.
27:40 Compare with the Direct study done in a power plant in Israel. Workers came to the plant, stayed all day, and the company provided lunch. Researchers designed three lunches: low-carb, low-fat, and an in-between Mediterranean-style diet. The workers ate whatever they wanted at home before they came to work and after. The only meal that was controlled was lunch. The study lasted two years.
28:22 Results? Rapid, sustained weight loss in those following the low-carb diet. Slower weight loss with the Mediterranean diet that ultimately caught up with the low-carb diet. The low-fat diet didn’t come close to the success of the other two. And remember, this was just by changing one meal per day.
29:05 The alternative theory says that consumption of easily digestible, highly processed carbs drives insulin up and sends the fat cells into a feeding frenzy. The results are that not only do we become more hungry, but we are stimulating the addiction centers in the brain, making these highly processed foods even more desirable for us. And as we’ve seen from the studies described above, this process drives food intake and lowers energy expenditure.
30:00 I’m not sure I’m buying the part about the 16 ounce steak.
30:15 Improving diet quality may be less arduous and more successful than calorie restriction over the long term.
I encourage you to watch the entire video, so you can get Dr. Ludwig’s arguments fully fleshed out and not just from my sketchy notes. Use those to review. If you want to read about these studies more in depth, take a look at Dr. Ludwig’s book Always Hungry? , which I reviewed here a little over a year ago.
As I said at the start, I pretty much agree with everything across the board with some minor exceptions. When you look at the study using the low-carb omelette as the control, you’ll see that subjects did better on that than on the slowly digested steel cut oats. Why not just eat the omelette and be done with it? If you just have to have oatmeal, go for the steel cut, of course, but I’d rather just opt for the omelette.
I found enlightening the notion that food palatability isn’t intrinsic to the food itself, but is more driven by the state of our brains and our level of satiation at any given time. I should have figured this out for myself based on one ill-fated fishing trip I went on as a teenager. A friend and I hiked up into the San Gabriel Mountains in Southern California to go fly fishing for trout. We were planning on spending the night and eating what we caught. Of course we caught nothing, but we ran into another fisherman who was pulling them in right and left. He obviously knew what he was doing while we didn’t.
We struck up a conversation with him about his technique and hung around watching him for a while trying to learn. He, too, was spending the night, so we all set up camp together. He fried up a couple of the trout he caught and asked us what we had brought to eat. We sheepishly told him we hadn’t brought anything, that we were going to eat what we caught. He said, “Bad move, boys.” He said he always brought something he didn’t like just in case he wasn’t successful. Then he would at least have something to eat, but would still he motivated to fish hard.
He then tossed us a couple of cans of Spam and told us to have at it. I’ve alway found Spam to be revolting, but I’ve got to tell you, that night I found it delicious beyond belief. So Dr. Ludwig is correct that the palatability is definitely not intrinsic to the food.
If you would like to see a longer talk by Dr. Ludwig, he is going to be on Detroit Public Television on Monday, March 13. The episode will be streamed live. Here is the promo for it: