 Nuts are packed with nutrition, but they're also packed with calories. Why then don't nuts seem to make people fat? This was a review published back in 2007, looking about 20 clinical trials that had been done on nuts and weight, and not a single one showed the weight gain one would expect. Some did show weight gain, but not as much as predicted. Add three handfuls of peanuts to people's daily diets for a few weeks, and they should gain like 8 pounds, but instead only gained about 2. What happened to the thousands of missing calories? Same thing with walnuts. After six months of a handful of walnuts a day, they should have gained about 12 pounds, but instead just gained 1, much lower than expected. Okay, what about two handfuls of nuts a day for six months? 40 to 50 almonds added to their diets every day. That's 320 calories added to their daily diet. They should have gained more than 16 pounds, but instead gained less than one. The women in the study only gained about a quarter of a pound. Wait a second, they stuffed their face with 40 to 50 nuts a day for six months and only gained a quarter of a pound? In fact, the weight gain in the study was so small, it wasn't even statistically significant, which means it may have just happened by chance. What happened to the tens of thousands of missing calories? The only other study showing weight gain found the same thing, five times less weight gain than expected, but unlike the other studies, these folks told eat the extra nuts, were also told to cut back on other foods, and so this one doesn't tell us much. Other studies adding nuts to people's diets showed no weight gain at all. One to two handfuls of walnuts added to daily diets for six weeks no weight gain. Then they put people on a low-fat diet and they lost weight. Now what happens when you add a handful or two of walnuts to that low-fat diet? No weight gain. What happened again to the missing calories? How about two to three handfuls of nuts? Three quarters of a cup of pecans added to their daily diet for eight weeks with 450 calories added to their daily diet. They should have gained about a pound a week, but didn't gain an ounce. That's 25,000 calories vanished into thin air. What happened? There was even a study in which adding daily handful of nuts for a month resulted in weight loss. Macadamia nuts this time, what is going on? All the other nuts studies in this review were what are called iso-energetic studies, meaning they adjusted the calories to ensure people would stay the same weight, which makes it even more remarkable than some of the studies people mysteriously lost more weight eating nuts. For example, here they prepared all the meals, forced people to eat only out of the metabolic kitchen in which food portions were calculated to the nearest gram. Both groups were given the same kind of diet, but one group was given handfuls of pecans. To ensure no weight changes, they made sure the diets had the same number of calories by reducing the portion sizes of the rest of the diet in the nut group. So in the end, each group was supposed to get 2,400 calories a day. Now when they chemically analyzed the diets, it turns out that the nut group ended up getting an extra 100 calories a day, which makes it even more crazy that the nut group lost weight. That's not supposed to happen. Another phenomenon here, people were given 400 calories of almonds, muffins, or half almonds, half muffins. Again, they tried to make all three diets the same number of calories, but the nut groups ended up with more calories, yet ended up the same or lower weight. How was that even possible? Well these were all clinical trials where people were put on added nuts for just a few weeks or months. What about long term? Maybe in the short run, nuts don't lead to weight gain, but maybe after years of eating nuts? Well that's been looked at six different ways. In studies lasting from one year to six years, the Harvard Nurses Health Study, one found no significant change. The other five out of six measures found significantly less weight gain and risk of abdominal obesity in those eating more nuts. This was published back in 2011 though. Is this just old news? And this was five years ago. Has there been any studies published since that are missing from these reviews? Yes, a whole bunch of them and I might as well just run through them quick. But I want to make sure to get through each one, so you have a kind of comprehensive sense of what's out there. Well, okay, remember that study where there were stuffing three handfuls of peanuts in their face every day and still didn't gain the expected weight? Well, nut calories may not count as much, but candy calories do. Two weeks of overfeeding with candy increases body weight, but the same amount of calories of nuts did not. So these peanuts may not make you gain weight, but these peanuts may. Then came pistachios versus pretzels, same amount of calories, but a significantly greater drop in body mass index in the pistachio group. In 2012, there was another pistachio study. Pistachios were randomized to consume either the recommended daily serving of 42 grams of pistachios, that's about 73 pistachios a day, versus a higher daily serving of all about 121 pistachios a day, or no pistachios for 12 weeks. Whoa, over 100 nuts a day they must have been packing on the pounds. Nope. Which is which? Does it matter? Can you even tell the zero nuts a day group from the 121 nuts a day group? How did 30,000 calories per person disappear? A cross-sectional study between nut intake and fatness, the skinniest people ate the most nuts, the fattest people ate the least nuts. Nut consumption was associated with a lower body mass index, and meat consumption was associated with a higher body mass index. In terms of people's waistlines, those eating the most nuts and vegetables had the slimmest waist, and those eating the most meat and meat products had the widest waist. They even calculated that each daily handful of nuts was associated with a 2 centimeter slimmer waist. Same thing found here in the US. Eating just a quarter ounce of nuts or more was associated with a significantly lower risk of being overweight and obese, though this was just for adults. There may be an opposite relationship for children, and you can see that the tree nuts and nut butters appeared to do better than when you include the peanuts and peanut butter. Then came more Harvard Action that published in the New England Journal of Medicine, weight gain most associated with junk food intake, potato chips, french fries, soda pop, and meat, and weight loss most associated with vegetables, nuts, whole grains, fruits, and surprisingly, yogurt. They think it may be due to the probiotics. The investigators conclude minimally processed foods such as nuts, fruits, vegetables, and whole grains should be increased. Indeed, global epidemics of obesity and chronic disease amplify. Both the health and economic imperatives of altering current agricultural and food industry priorities, many small dietary and lifestyle changes together, can make a big difference for good, for bad, or good, and for nuts, it was good. Here's the latest review on nuts published in 2012. We're finally getting to the end, sorry for this long video. Which concluded, in human supplementation studies, nuts have been shown to improve cholesterol and arterial function and reduce inflammation all without causing weight gain. And finally, three last papers published not just 2012, but actually August 2012. The first was a comparison of a low-calorie diet with or without nuts, and though at first it looked like the nut-free diet was going to win out, by the end of the study, 18 months, no significant difference was found. Then two weeks ago, another cross-sectional study, meat, soda, and cake, were associated with the highest BMI and nut consumption with the lowest. Similar to what was concluded in the latest review on food and long-term weight change over time, they looked at all the best studies published over the last 12 years, and what did they find? They found two main things. No evidence for high intake of dietary fiber and nuts predicting less weight gain over time, and for high intake of meat predicting more weight gain. The bottom line is that so far every single study, in which they added nuts to people's diets without trying to restrict calories, failed to show the expected weight gain, whether it was just less than predicted, no weight gain at all, or even lost weight. So what happened to the missing calories? Well, the mystery has been solved. On Monday I presented the pistachio principle and the fecal excretion theory. On Tuesday they were put to the test. On Wednesday I explored the dietary compensation theory, and by Thursday we had figured it out. Part of the trick seemed to be that nuts boosted fat burning within the body, but how? Well, it could be the arginine, or, spoiler alert, the flavonoid phytonutrients, as we'll see in Monday's video of the day.