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Ep. 42 – Calorie loss in stool

Did you know that we lose calories every day in our stool? Today on Straight Talk on Health Dr. Chet Zelasko reviews the latest research that gives us the scoop on poop

Welcome to Straight Talk on Health. I’m your host Dr. Chet Zelasko. Straight Talk on Health is recorded in conjunction with WGVU in Grand Rapids MI. I examine the world of health. Whether it’s research that makes the news, another miracle diet, or a new food fad, I look at the science behind them, and let you know whether it’s real or not. You can check out other things that I do on my website drchet.com and sign up for my free emails.

Ask and you shall receive. In the last podcast about UPFs, I posed the question on whether there is a difference in absorbing calories from UFPs compared to less processed foods. No longer had I had written the script for that podcast when another research paper was published that suggested maybe there was. Time for the scoop on poop.

In my examination of the research on UFP, I’ve found out that we consume more calories and that we absorb more calories if we eat large amounts UFP. The final question that I couldn’t answer was this: is there any research that suggested a calorie is not a calorie. In other words, would we somehow extract more calories from UPF than from less processed food? Or, perhaps, do we actually lose more calories if we eat less UFP? In other words, do we actually eliminate calories if we eat a diet that is less processed? More fiber. More resistant starch. This was really interesting to find that we actually may not absorb every calorie we consume! I have to admit that this one evaded me. I didn't realize that we lost calories in our stool under healthy conditions.

Researchers wanted to test whether diet could influence the number of calories lost in feces among a variety of other things. The researchers recruited 17 healthy normal weight to overweight men and women an average age of 31 years old. They designed a diet that could enhance the microbiome by feeding the healthy microbes that reside in the colon. They matched the diet for calorie and macronutrient percentages with a Westernized diet. The major difference was the fiber content and resistant starch level. The Western diet included more highly processed foods.

At different points in the study, on both types of diets, they measured the exact calories consumed, calories used in exercise, rest, and sleep, and collected all urine and stool for 24 hours. Collecting the urine and stool samples is obvious but how do precisely measure calories burned in all activities including sleep. They have them stay in a metabolic chamber which can measure changes in heat as well as changes in the O2-CO2 content of the room. With those pieces of information, they can calculate the number of calories a person uses.

Think of a small studio apartment with a treadmill (they have to calculate the heat generated from the motor as well as anything that can generate heat to account for it), a desk, a bed, a bathroom, and a way to get meals in and out without changing the atmosphere of the metabolic chamber. Really cool stuff to us exercise physiologists.

They found many things. Subjects ate the same number of calories on either diet. That was the goal. The macronutrient distribution was the same on either diet. The most significant difference between the diet was the fiber content and the resistant starch content. The diet high in UPFs food had little fiber or resistant starch.

The most interesting observation was that the diet increased the calories lost in the stool by an average of 116 calories per day. Why? The bacteria were using the fiber and resistant starch to manufacture more metabolizable calories, specifically short chain fatty acids, but the microbes in the colon made so much extra that the extra calories were lost in feces and therefore, not absorbed. Wow! I mean really, wow! The answer to my question is not that there more calories in UPFs; it was the things missing from those foods that inevitably led to a loss of more calories even though the bacteria were making more of them via fermentation.

But wait, there's more. When looking at the methods section in detail, there is one other thing that the researchers did. They kept the food particles as large as is comfortably possible. That means steak instead of hamburger meat. It means whole grain breads instead of plain white flour breads. I never thought of it this way before but UPFs does replace the natural chewing and enzyme breakdown that occurs in the first part of the small intestine. It's not necessary because the particles are small once they exit the stomach. Keeping the size of food particles larger causes the actual digestion process to begin earlier in the digestive system.

What else did they show? Looking at the satiety hormones, pancreatic polypeptide and GLP-1 decreased while leptin increased on the UFPs diet. With the higher fiber and resistant starch diet, the opposite happened. There were no differences on either diet with energy expenditure, the amount of food eaten, the levels of hunger and satiety, the rate of gastric emptying nor the transit time through the entire digestive system.

There were definite improvements in the microbiome that decreased the ability of a person to absorb and use energy because of the loss of the calories in the stool. Just the opposite happened on the UPFs. It increased the amount of metabolizable energy in the small intesting. When you think about it, that's pretty amazing. People weren't extracting more calories even though we know more calories are absorbed from UPFs Rather it was the loss of calories after feeding the bacteria who responded by fermenting more calories like crazy so that the calories were never absorbed. Wow!

This look at UPF has been interesting. It’s easy to be a demagogue and condemn as so many others have based on a few studies. In spite of the research that's been done, all of the clinical trials on UPF are on small groups of subjects. We still don't have an actual answer when it comes to weight loss. Is a calorie still just calorie? That study has still yet to be done.

Here are some additional thoughts. I'm not sure that breaking things down into the smallest components using manual cutters is beneficial for absorption or not. That’s the implication in a well-known and pervasive marketing message of a brand of fruit and vegetable supplements sold in capsule form. The powder that results from dehydrating the fruits and vegetables and cutting them up into the finest of powder helps with them absorb better. Can it break it down fine enough to really help absorption? After all, there are no real macronutrients in those powders according to the label. Phytonutrients are absorbed by processes that bear no similarity to protein, carbohydrates, or fats.

Not all UPF are bad, either. Remember that protein powder is a highly processed food, whether from animal or plant sources. So is stevia, the “natural” sweetener. How about almond milk? Have you ever seen an almond teat? Neither have I.

What we need today, not in 1900, 1930, 1950, or even the 1970s, is a balanced approach to nutritional intake. It’s as simple as eat better, but it doesn’t have to be perfect. Eat less, but don’t starve yourself on foods you don’t like. And move more. It’s as simple as that. Until next time this is Dr. Chet Zelasko saying health is a choice people. Choose wisely today and every day.

1. Food Funct. 2016 May 18;7(5):2338-46. doi: 10.1039/c6fo00107f.

2. Food Funct 2017 Feb 22;8(2):651-658. doi: 10.1039/c6fo01495j.

3. https://doi.org/10.1016/j.cmet.2019.05.008

4. https://doi.org/10.1016/j.cmet.2019.05.008

5. https://doi.org/10.1038/s41467-023-38778-x

Dr. Chet Zelasko is a scientist, speaker, and author. Dr. Chet has a Ph.D. and MA in Exercise Physiology and Health Education from Michigan State University and a BS in Physical Education from Canisius College. He’s certified by the American College of Sports Medicine as a Health and Fitness Specialist, belongs to the American Society of Nutrition, and has conducted research and been published in peer-reviewed journals. You can find him online at drchet.com.
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