Losing Weight with Fiber-Rich Foods

**Michael Greger** (0:00)
Trying to stay healthy can seem like a full-time job sometimes, especially with all the conflicting information that's out there, but I'm here to make that job a little easier. Welcome to the Nutrition Facts Podcast. I'm your host, Dr. Michael Greger.
Did you know that a single dietary change could increase our resting metabolic rate? Here is our story with Nutrition Facts senior research scientist, Dr. Christine Dennis.

**Christine Dennis** (0:27)
We now know why fiber-rich foods can have such a powerful effect on our weight. The evidence for the role of fiber in weight control started with so-called ecological studies. These involve comparing population averages. And researchers noted that populations with extraordinary fiber intakes tend to have negligible obesity rates. For example, the average Pima Indian in Mexico, eating their traditional high-fiber diet centered around the three sisters— corn, beans, and squash—is normal weight. But the average Pima on US reservations has obesity. The problem with dealing with population averages is that we don't know if the individuals eating the higher-fiber diets are themselves necessarily the ones protected from obesity. What do we see in cohort studies where individuals and their diets are followed over time? A cohort study of overweight youth found that the amount of fiber found in a single half-cup daily serving of beans—about 6 grams—over about a two-year period was associated with a profound 25% difference in abdominal obesity.
In about the same time frame in middle-age women, each two-gram increase in daily fiber was associated with a weight decrease of about a pound.
The postpartum period seems to be a critical time for women to be at risk of retaining the weight put on during pregnancy. A study of hundreds of new moms followed for the first five months found that inadequate fiber intake appeared to increase obesity risk by 24%.
And it's not just women. A cohort that included tens of thousands of men followed for years concluded that an increase in fiber consumption of just 10 grams a day may prevent about 10% of weight gain within the population. Overall, the evidence from these kinds of observational studies is strong that increasing consumption of dietary fiber with fruits, vegetables, whole grains, and legumes across the life cycle is a critical step in stemming the epidemic of obesity. These studies can control for non-dietary influences such as physical activity by equipping people with gadgets to measure their movement. But there may be uncontrolled confounding dietary factors. Think about the list of high-fiber foods, fruits, vegetables, whole grains, and beans. Maybe fiber intake is just a marker for the intake of healthy foods. And there are dozens of reasons why eating whole plant foods could lead to weight loss that have nothing to do with fiber. To know if there's a cause and effect relationship between fiber and weight loss, you need to put it to the test in interventional trials. That's where colonic infusions can come in handy. In a randomized double-blind placebo-controlled crossover study, researchers showed that people's metabolism can be boosted within 30 minutes of an infusion into their rectums of short-chain fatty acids. The molecules our gut bacteria make when we feed them fiber. The study used the amounts we'd expect to create ourselves just from eating a fat-fiber diet. Not only did the study participants get an increase in their resting metabolic rate, the amount of calories burned just by existing, but specifically their fat oxidation shot up as well, increasing the amount of fat they were burning by more than 25%.
This translates to about an extra third of a pat of butter's worth of fat burned off their body within two hours of the infusion. Colonic catheters aside, we can get short-chain fatty acids directly and get the same little bump in resting metabolic rate and whole-body fat breakdown, in addition to a decrease in appetite. So again, fiber may work on both sides of the energy balance equation, but does that decreased appetite actually translate into eating less? We'll find out next.
How does the fiber we eat in foods impact our appetites and our resting metabolic rate, the amount of calories burned just by existing? What happens when we eat fiber-filled foods like beans?
Researchers in Sweden gave people beans for supper, and by the next morning, after their friendly flora had a chance to eat them too, their satiety hormones like PYY were up, their hunger hormone ghrelin was down, and they reported feeling less hungry.
The researchers didn't measure subsequent food intake, but a similar study with whole-grain rye for supper did, and found a decrease in food intake at lunch the next day. Those who had eaten the fiber-rich food the night before felt fully satiated with about 100 fewer calories at a meal more than 12 hours later. So by eating fiber-rich foods, you're setting yourself up for success.