metabolism
Ultra-Processed Diet Leads to Extra Calories, Weight Gain
Posted on by Dr. Francis Collins
If you’ve ever tried to lose a few pounds or just stay at a healthy weight, you’ve likely encountered a dizzying array of diets, each with passionate proponents: low carb, low fat, keto, paleo, vegan, Mediterranean, and so on. Yet most nutrition experts agree on one thing: it’s best to steer clear of ultra-processed foods. Now, there’s some solid scientific evidence to back up that advice.
In the first randomized, controlled study to compare the effects of ultra-processed with unprocessed foods, NIH researchers found healthy adults gained about a pound per week when they were given a daily diet high in ultra-processed foods, which often contain ingredients such as hydrogenated fats, high fructose corn syrup, flavoring agents, emulsifiers, and preservatives. In contrast, when those same people ate unprocessed whole foods, they lost weight.
Intriguingly, the weight differences on the two diets occurred even though both kinds of foods had been carefully matched from a nutritional standpoint, including calorie density, fiber, fat, sugar, and salt. For example, breakfast for the ultra-processed group might consist of a bagel with cream cheese and turkey bacon, while the unprocessed group might be offered oatmeal with bananas, walnuts, and skim milk.
The explanation for the differences appears to lie in the fact that study participants were free to eat as little or as much food as they wished at mealtimes and to snack between meals. It turns out that when folks were on the ultra-processed diet they ate significantly more—about 500 extra calories per day on average—than when they were on the unprocessed diet. And, as you probably know, more calories without more exercise usually leads to more weight!
This might not seem new to you. After all, it has been tempting for some time to suggest a connection between the rise of packaged, ultra-processed foods and America’s growing waistlines. But as plausible as it might seem that such foods may encourage overeating, perhaps because of their high salt, sugar, and fat content, correlation is not causation and controlled studies of what people actually eat are tough to do. As a result, definitive evidence directly tying ultra-processed foods to weight gain has been lacking.
To explore the possible connection in the study now reported in Cell Metabolism, researchers at NIH’s National Institute of Diabetes and Digestive and Kidney Diseases took advantage of the Metabolic Clinical Research Unit at the NIH Clinical Center, Bethesda, MD. The unit is specially equipped to study issues involving diet and metabolism.
The researchers asked 20 healthy men and women of stable weight to stay at the center for 28 days. Each volunteer was randomly assigned to eat either an ultra-processed or unprocessed diet for two consecutive weeks. At that point, they switched to the other diet for another two weeks.
Both diets consisted of three daily meals, and volunteers were given permission to eat as much food as they liked. Importantly, a team of dieticians had carefully designed the ultra-processed and unprocessed meals such that they were well matched for total calories, calorie density, macronutrients, fiber, sugars, and salt.
At lunch, for example, one of the study’s processed meals consisted of quesadillas, refried beans, and diet lemonade. An unprocessed lunch consisted of a spinach salad with chicken breast, apple slices, bulgur, and sunflower seeds with a side of grapes.
The main difference between each diet was the proportion of calories derived from ultra-processed versus unprocessed foods as defined by the NOVA diet classification system. This system categorizes food based on the nature, extent, and purpose of food processing, rather than its nutrient content.
Each week, researchers measured the energy expenditure, weight, and changes in body composition of all volunteers. After two weeks on the ultra-processed diet, volunteers gained about two pounds on average. That’s compared to a loss of about two pounds for those on the unprocessed diet.
Metabolic testing showed that people expended more energy on the ultra-processed diet. However, that wasn’t enough to offset the increased consumption of calories. As a result, participants gained pounds and body fat. The study does have some limitations, such as slight differences in the protein content of the two diets. and the researchers plan to address such issues in their future work.
During this relatively brief study, the researchers did not observe other telltale changes associated with poor metabolic health, such as a rise in blood glucose levels or fat in the liver. While a couple of pounds might not sound like much, the extra calories and weight associated with an ultra-processed diet would, over time, add up.
So, it appears that a good place to start in reaching or maintaining a healthy weight is to follow the advice shared by all those otherwise conflicting diet plans: work to eliminate or at least reduce ultra-processed foods in your diet in favor of a balanced variety of unprocessed, nutrient-packed foods.
Reference:
[1] Ultra-processed diets cause excess calorie intake and weight gain: An inpatient randomized controlled trial of ad libitum food intake. Hall KD et al. Cell Metab. 2019 May 16.
Links:
Obesity (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)
Healthy Eating Plan (National Heart, Lung, and Blood Institute/NIH)
Body Weight Planner (NIDDK/NIH)
Kevin D. Hall (NIDDK/NIH)
Metabolic Clinical Research Unit (NIDDK/NIH)
NIH Support: National Institute of Diabetes and Digestive and Kidney Diseases
‘Exercise Hormone’ Tied to Bone-Strengthening Benefits
Posted on by Dr. Francis Collins
There’s no doubt that exercise is good for us—strengthening our muscles, helping us maintain a healthy weight, maybe even boosting our moods and memories. There’s also been intriguing evidence that exercise may help build strong bones.
Now, an NIH-funded study is shedding light on the mechanism behind exercise’s bone-strengthening benefits [1]. The new work—which may lead to new approaches for treating osteoporosis, a disease that increases the risk of bone fracture—centers on a hormone called irisin that is secreted by muscles during exercise.
In a series of mouse experiments, the researchers found that irisin works directly on a common type of bone cell, stimulating the cells to produce a protein that encourages bones to thin. However, this chain of molecular events ultimately takes a turn for the better and reverses bone loss.
Bruce Spiegelman’s lab at the Dana-Farber Cancer Institute and Harvard University Medical School, Boston, first discovered the irisin hormone in 2012 [2]. In the years since, evidence has accumulated suggesting a connection between irisin and many of the benefits that come with regular workouts. For example, delivering low doses of irisin—sometimes called “the exercise hormone”—increase bone density and strength in mice.
But how does irisin act on bones? The answer hasn’t been at all clear. A major reason is the protein receptor on our cells that binds and responds to irisin wasn’t known.
In the new study reported in the journal Cell, Spiegelman’s team has now identified irisin’s protein receptor, called αVβ5 integrin. Those receptors are present on the surface of osteocytes, the most common cell type found in mature bone tissue.
The researchers went on to show that irisin helps osteocytes to live longer. It also leads the bone cells to begin secreting a protein called sclerostin, known for its role in preparing bones for remodeling and rebuilding by first breaking them down. Interestingly, previous studies also showed sclerostin levels increase in response to the mechanical stresses that come with exercise.
To further explore the role of irisin in mouse studies, the researchers gave the animals the hormone for six days. And indeed, after the treatment, the animals showed higher levels of sclerostin in their blood.
The findings suggest that irisin could form the basis of a new treatment for osteoporosis, a condition responsible for almost nine million fractures around the world each year. While it might seem strange that a treatment intended to strengthen bone would first encourage them to break down, this may be similar to the steps you have to follow when fixing up a house that has weakened timbers. And Spiegelman notes that there’s precedent for such a phenomenon in bone remodeling—treatment for osteoporosis, parathyroid hormone, also works by thinning bones before they are rebuilt.
That said, it’s not yet clear how best to target irisin for strengthening bone. In fact, locking in on the target could be a little complicated. The Speigelman lab found, for example, that mice prone to osteoporosis following the removal of their ovaries were paradoxically protected from weakening bones by the inability to produce irisin.
This new study fits right in with other promising NIH-funded efforts to explore the benefits of exercise. One that I’m particularly excited about is the Molecular Transducers of Physical Activity Consortium (MoTrPAC), which aims to develop a comprehensive map of the molecular changes that arise with physical activity, leading to a range of benefits for body and mind.
Indeed, the therapeutic potential for irisin doesn’t end with bone. In healthy people, irisin circulates throughout the body. In addition to being produced in muscle, its protein precursor is produced in the heart and brain.
The hormone also has been shown to transform energy-storing white fat into calorie-burning brown fat. In the new study, Spiegelman’s team confirms that this effect on fat also depends on the very same integrin receptors present in bone. So, these new findings will no doubt accelerate additional study in Speigelman’s lab and others to explore the many other benefits of irisin—and of exercise—including its potential to improve our moods, memory, and metabolism.
References:
[1] Irisin Mediates Effects on Bone and Fat via αV Integrin Receptors. Kim H, Wrann CD, Jedrychowski M, Vidoni S, Kitase Y, Nagano K, Zhou C, Chou J, Parkman VA, Novick SJ, Strutzenberg TS, Pascal BD, Le PT, Brooks DJ, Roche AM, Gerber KK, Mattheis L, Chen W, Tu H, Bouxsein ML, Griffin PR, Baron R, Rosen CJ, Bonewald LF, Spiegelman BM. Cell. 2018 Dec 13;175(7):1756-1768.
[2] A PGC1-α-dependent myokine that drives brown-fat-like development of white fat and thermogenesis. Boström P, Wu J, Jedrychowski MP, Korde A, Ye L, Lo JC, Rasbach KA, Boström EA, Choi JH, Long JZ, Kajimura S, Zingaretti MC, Vind BF, Tu H, Cinti S, Højlund K, Gygi SP, Spiegelman BM. Nature. 2012 Jan 11;481(7382):463-8.
Links:
Osteoporosis (NIH)
Guide to Physical Activity (National Heart, Lung, and Blood Institute/NIH)
Spiegelman Lab (Dana-Farber Cancer Institute, Boston)
Molecular Transducers of Physical Activity in Humans (Common Fund/NIH)
Video: MoTrPAC (Common Fund)
NIH Support: National Institute of Diabetes and Digestive and Kidney Diseases; National Heart, Lung, and Blood Institute; National Institute on Aging; National Institute of Neurological Disorders and Stroke
Has an Alternative to Table Sugar Contributed to the C. Diff. Epidemic?
Posted on by Dr. Francis Collins
Thinkstock/piyaphat50
Most of us know how hard it is to resist the creamy sweetness of ice cream. But it might surprise you to learn that, over the past 15 years or so, some makers of ice cream and many other processed foods—from pasta to ground beef products—have changed their recipes to swap out some of the table sugar (sucrose) with a sweetening/texturizing ingredient called trehalose that depresses the freezing point of food. Both sucrose and trehalose are “disaccharides.” Though they have different chemical linkages, both get broken down into glucose in the body. Now, comes word that this switch may be an important piece of a major medical puzzle: why Clostridium difficile (C. diff) has emerged as a leading cause of hospital-acquired infections.
A new study in the journal Nature indicates that trehalose-laden food may have helped fuel the recent epidemic spread of C. diff., which is a microbe that can cause life-threatening gastrointestinal distress, especially in older patients getting antibiotics and antacid medicines [1, 2]. In laboratory experiments, an NIH-funded team found that the two strains of C. diff. most likely to make people sick possess an unusual ability to thrive on trehalose, even at very low levels. And that’s not all: a diet containing trehalose significantly increased the severity of symptoms in a mouse model of C. diff. infection.
Creative Minds: Potential Diabetes Lessons from Binge-Eating Snakes
Posted on by Dr. Francis Collins
Stephen Secor/Credit: Secor Lab
Many people would do just about anything to avoid an encounter with a snake. Not Stephen Secor. Growing up in central New York State, Secor was drawn to them. He’d spend hours frolicking through forest and field, flipping rocks and hoping to find one. His animal-loving mother encouraged him to keep looking, and she even let him keep a terrarium full of garter snakes in his bedroom. Their agreement: He must take good care of them—and please make sure they don’t get loose.
As a teen, Secor considered a career as a large-animal veterinarian. But a college zoology course led him right back to his fascination with snakes. Now a professor at the University of Alabama, Tuscaloosa, he’s spent 25 years trying to understand how some snakes, such as the Burmese python shown above, can fast for weeks or even months, and then go on a sudden food binge. Secor’s interest in the feast-or-famine digestive abilities of these snakes has now taken an unexpected turn that he never saw coming: a potential treatment to help people with diabetes.
Protein Links Gut Microbes, Biological Clocks, and Weight Gain
Posted on by Dr. Francis Collins
Caption: Lipids (red) inside mouse intestinal cells with and without NFIL3.
Credit: Lora V. Hooper, University of Texas Southwestern Medical Center, Dallas
The American epidemic of obesity is a major public health concern, and keeping off the extra pounds is a concern for many of us. Yet it can also be a real challenge for people who may eat normally but get their days and nights mixed up, including night-shift workers and those who regularly travel overseas. Why is that?
The most obvious reason is the odd hours throw a person’s 24-hour biological clock—and metabolism—out of sync. But an NIH-funded team of researchers has new evidence in mice to suggest the answer could go deeper to include the trillions of microbes that live in our guts—and, more specifically, the way they “talk” to intestinal cells. Their studies suggest that what gut microbes “say” influences the activity of a key clock-driven protein called NFIL3, which can set intestinal cells up to absorb and store more fat from the diet while operating at hours that might run counter to our fixed biological clocks.
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