Fri, Jan-22-21, 07:15
NIH study compares low-fat, plant-based diet to low-carb, animal-based diet
NIH study compares low-fat, plant-based diet to low-carb, animal-based diet
People on a low-fat, plant-based diet ate fewer daily calories but had higher insulin and blood glucose levels, compared to when they ate a low-carbohydrate, animal-based diet, according to a small but highly controlled study at the National Institutes of Health. Led by researchers at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the study compared the effects of the two diets on calorie intake, hormone levels, body weight, and more. The findings, published in Nature Medicine(link is external), broaden understanding of how restricting dietary carbohydrates or fats may impact health.
“High-fat foods have been thought to result in excess calorie intake because they have many calories per bite. Alternatively, high-carb foods can cause large swings in blood glucose and insulin that may increase hunger and lead to overeating,” said NIDDK Senior Investigator Kevin Hall, Ph.D., the study’s lead author. “Our study was designed to determine whether high-carb or high-fat diets result in greater calorie intake.”
The researchers housed 20 adults without diabetes for four continuous weeks in the NIH Clinical Center’s Metabolic Clinical Research Unit. The participants, 11 men and nine women, received either a plant-based, low-fat diet or an animal-based, low-carbohydrate diet for two weeks, immediately followed by two weeks on the alternate diet. The low-fat diet was high in carbohydrates. The low-carbohydrate diet was high in fats. Both diets were minimally processed and had equivalent amounts of non-starchy vegetables. The participants were given three meals a day, plus snacks, and could eat as much as desired.
The main results showed that people on the low-fat diet ate 550 to 700 fewer calories per day than when they ate the low-carb diet. Despite the large differences in calorie intake, participants reported no differences in hunger, enjoyment of meals, or fullness between the two diets. Participants lost weight on both diets, but only the low-fat diet led to a significant loss of body fat.
“Despite eating food with an abundance of high glycemic carbohydrates that resulted in pronounced swings in blood glucose and insulin, people eating the plant-based, low-fat diet showed a significant reduction in calorie intake and loss of body fat, which challenges the idea that high-carb diets per se lead people to overeat. On the other hand, the animal-based, low-carb diet did not result in weight gain despite being high in fat,” said Hall.
These findings suggest that the factors that result in overeating and weight gain are more complex than the amount of carbs or fat in one’s diet. For example, Hall’s laboratory showed in 2019 that a diet high in ultra-processed food led to overeating and weight gain in comparison to a minimally processed diet matched for carbs and fat.
The plant-based, low-fat diet contained 10.3% fat and 75.2% carbohydrate, while the animal-based, low-carb diet was 10% carbohydrate and 75.8% fat. Both diets contained about 14% protein and were matched for total calories presented to the subjects, although the low-carb diet had twice as many calories per gram of food than the low-fat diet. On the low-fat menu, dinner might consist of a baked sweet potato, chickpeas, broccoli and oranges, while a low-carb dinner might be beef stir fry with cauliflower rice. Subjects could eat what and however much they chose of the meals they were given.
“Interestingly, our findings suggest benefits to both diets, at least in the short-term. While the low-fat, plant-based diet helps curb appetite, the animal-based, low-carb diet resulted in lower and more steady insulin and glucose levels,” Hall said. “We don’t yet know if these differences would be sustained over the long term.”
The researchers note that the study was not designed to make diet recommendations for weight loss, and results may have been different if participants were actively trying to lose weight. Further, all meals were prepared and provided for participants in an inpatient setting, which may make results difficult to repeat outside the lab, where factors such as food costs, food availability, and meal preparation constraints can make adherence to diets challenging. The tightly controlled clinical environment, however, ensured objective measurement of food intake and accuracy of data.
“To help us achieve good nutrition, rigorous science is critical − and of particular importance now, in light of the COVID-19 pandemic, as we aim to identify strategies to help us stay healthy,” said NIDDK Director Griffin P. Rodgers, M.D. “This study brings us closer to answering long-sought questions about how what we eat affects our health.”
The research was supported by the NIDDK Intramural Research Program. Additional NIH support came from the National Institute of Nursing Research under grant 1Z1ANR000035-01.
Low-carb diets seem to involve more calories than low-fat diets
People who follow a low-carb diet consume more calories on average than those who follow a low-fat diet, according to a new study, although both diets can result in similar levels of total weight loss.
“There [are] benefits for both of these diets,” says Kevin Hall at the National Institute of Diabetes and Digestive and Kidney Diseases in Maryland. “It’s a lot more complicated than a lot of the diet gurus and folks would have you believe.”
Hall and his colleagues studied 20 volunteers who were admitted to a clinic for the duration of the study. Ten were put on a plant-based, low-fat diet for two weeks and the other 10 were placed on an animal-based, ketogenic, low-carb diet. After two weeks on one diet, the participants were swapped to the other diet for a further two weeks.
Participants were free to eat as much as they wanted from whichever diet they were on, and Hall and his team monitored their calorie intake as well as their weight, body fat and insulin levels after meals.
On both diets, volunteers lost between 1 and 2 kilograms, on average, but people on the low-fat diet consumed fewer calories and lost body fat at a higher rate than people who followed the low-carb diet. However, those on the low-carb diet experienced less variability in blood sugar and insulin levels after meals.
“It’s a mixed bag,” says Hall. “If you think that large swings in glucose and insulin are potentially harmful, then the ketogenic diet came out the winner,” he says. “But there are benefits to the low-fat diet – they lost a greater percentage of their weight coming from body fat.”
“Maybe studies like this can help us distinguish between what diets are better targeted to different people,” says Hall. “If you think your insulin surges are particularly harmful, then the ketogenic diet might be for you. If you’re worried about triglyceride [a constituent of fat] levels in your blood going up too high after meals, then clearly the low-fat diet was better.”
David Unwin, a family doctor at Norwood surgery in Southport, UK, points out that two weeks may not be enough time for volunteers to adapt to a ketogenic diet. It will be important to investigate the longer-term effects of both diets, he says.
Whatever dietary option someone chooses, regular feedback from healthcare providers can be important. “In clinical practice, I find it works so well to support people in their dietary choices whilst supplying feedback as to how their metabolic health is progressing,” says Unwin.
Journal reference: Nature Medicine, DOI: 10.1038/s41591-020-01209-1
Is keto really better for weight loss? A new study takes a closer look at the diet.
There’s a lot of competition for the most contentious issue in weight loss, but I’d have to give the nod to ketogenic diets. Now a study about them sheds some interesting new light — although I’m not holding out hope for kumbaya.
First though, a brief overview of the theory of ketogenic diets. When you eat carbohydrates, your body processes them with insulin, which shuttles blood glucose into fat stores, leaving you hungry. If you don’t eat many carbs, your body starts running on ketones, which your liver manufactures from fat — less hunger, less fat accumulation. Or that’s the theory, at any rate.
It’s important to keep in mind that nothing, including keto diets, can defeat the calorie balance equation: To lose weight, you have to burn more calories than you absorb. But there are two mechanisms by which a keto diet might help you do that: It could leave you satiated on fewer calories, so you take in less, and it could increase the rate at which your body burns energy, so you expend more.
Does keto actually do those things?
Let’s take appetite first, which brings us back to that interesting new study. It’s by the National Institutes of Health’s Kevin Hall, the same scientist who found that people eating ultra-processed food ate 500 calories more per day than people eating a diet of whole-ish foods. This time, he compared a keto diet to a low-fat, high-carb plant-based diet.
If you’re of a certain age, you may recall that low-fat diets have their own theory, about which much was made back in the ’90s. Because fat is calorie-dense — nine calories per gram vs. four for carbs and protein — high-fat diets lead to overconsumption. Hall’s study wanted to test the battling theories by comparing the diets head-to-head.
Twenty subjects, in-patients at a NIH facility so all their consumption could be monitored, were fed either the keto diet or the low-fat diet for two weeks, and then switched over to the other. (These studies are very expensive, which is why they tend to be small and short.)
Which diet led to less consumption?
The low-fat. By a lot: nearly 700 calories per day. This, despite the fact that insulin levels on the low-fat diet were, Hall told me, “through the roof.” The low-fat group also lost a little more fat (only about a pound, not enough for statistical significance). The keto group lost more fat-free mass, but Hall points out that a big component of that is water, which you always lose when you cut carbs.
Why ‘moderation’ is the worst weight-loss advice ever
But wait! This is not the last nail in the coffin of keto satiety. Hall made a point of highlighting the fact that, on the keto diet, consumption dropped by 300 daily calories in the second week, possibly because of a satiety effect kicking in. Would it have dropped more had the study gone longer? There’s no way to know, but it’s certainly possible. A 2015 meta-analysis of studies of satiety on keto vs. other diets found that keto was indeed somewhat more satiating, and Hall told me that the theory that being in ketosis suppresses hunger could also explain why some subjects in studies of fasting report not being hungry.
Another piece of evidence comes from Hall’s previous study, the one about processed foods.
The energy density of the keto diet in the new study was comparable to that of the highly processed diet in his previous study, Hall said, but subjects on the keto diet didn’t overeat, while subjects on the processed diet did.
I think it’s safe to say that the preponderance of the evidence indicates that keto diets may indeed be more satiating than some other diets.
So let’s move on to the second question: Does eating keto up your energy expenditure?
Hall has researched that, too. In a study he conducted, he found that energy expenditure increased 57 calories per day on the keto diet, although there was no accompanying fat loss. In a review he did of other studies, though, he found no advantage.
There are studies that find that keto diets increase energy expenditure, and the issue is very contentious. Scientists argue about methodology and accuracy and the various ways to measure energy expenditure, and I don’t think there’s a clear consensus. Me, I’m absolutely ready to believe that energy expenditure can vary on different diets, because our bodies handle different foods in different ways, but I think it’s unlikely that the difference will be big enough to matter much. If keto diets make you burn, say, several hundred more calories every day, it shouldn’t be that hard to detect it in the lab.
So where does that leave us? Ketogenic diets may suppress appetite, at least a little, and they may even help you burn more calories. In practice, though, they don’t do better than other diets in the long term. In the short term, several studies have found that keto dieters lose more weight. A 2013 review found that, among studies that followed people for at least a year, keto dieters lost about two pounds more than low-fat dieters, a finding the authors called “of little clinical significance.” In 2019, the National Lipid Association concluded: “Low-CHO [carbohydrate] and very-low-CHO diets are not superior to other dietary approaches for weight loss.”
I talked to Gary Taubes about this. He’s a journalist who has written about low-carb diets for a long time, and his latest book, “The Case for Keto,” came out in December. A ketogenic diet is very compelling to him, in part because he was able to manage his own weight on a low-carb diet after having failed with other diets.
Diet trials, he pointed out, don’t test diets; they test diet advice. Unless you lock people up and control what they eat, which you can only do for short periods, part of what you’re testing in a diet trial is how well someone can follow the program. Almost all diets fail because people can’t follow them, and keto is no exception. I asked Christopher Gardner of Stanford University, who has conducted some of the most robust diet trials ever done, and obesity researcher Stephan Guyenet, author of “The Hungry Brain,” whether they think ketogenic diets outperform other diets in weight-loss trials, and both said no. (There may be benefits for management of diabetes or other medical conditions, but I’m using up all my 1,200 words on weight loss.)
But Guyenet added that the trials of keto diets have established something important. “If you went back 20 or 30 years and asked the average obesity researcher or doctor about a diet that’s high in fat and low in carbs, I think they’d say that would be disastrous, it would lead to obesity and heart disease,” he told me. “The biggest update is that it doesn’t. It’s not catastrophic for your health, and it may have some benefits. The predicted adverse effects haven’t materialized.” Although we don’t have enough information to say for sure that keto is safe in the long run, so far it looks fine.
There’s one more thing. If you look outside controlled trials, you find a whole lot of very enthusiastic keto advocates. “Where does this passion come from?” Taubes asked me, and I think it’s a good question. For people who succeed, keto is very, very compelling — as anyone on social media is likely to hear. Finding an online community that’s supportive and encouraging is bound to help some people stick with it, and that continued success lends resonance to the enthusiasm. Sometimes, though, that community crosses the line, and outlandish keto claims abound. Guyenet told me he’s gotten thank-yous from ex-ketoers for “helping them get out of the cult.”
If keto works for you, I’m delighted! If it doesn’t, you’re not alone. The only sure thing in diets is that there’ll be a new one as soon everyone’s tired of this one.