The more you eat, the thinner you get? Are there really negative calorie foods?

Author: cryalex (Shanghai Science and Technology Education Press)

The article comes from the Science Academy official account (ID: kexuedayuan)

It has been widely circulated on the Internet that there are some foods that produce less energy when eaten than the energy required to be digested, thus consuming the body's calories and achieving the effect of weight loss. Such foods are called negative calorie foods.

The more you eat foods like vegetables, fruits and nuts, the faster you lose weight. The reason those who claim that negative calorie foods are effective is that these foods have a lot of fiber, and fiber does not provide energy to our body, but the body will use some of the energy to break it down...

It sounds reasonable at first, but is it really so?

(Image source: https://www.fabiaoqing.com/biaoqing/detail/id/572898.html)

It's not enough to just talk, you have to show experimental results

There are already many related rumor-refuting posts on the Internet, most of which are theoretical analysis. Dialectical materialism believes that practice is the only criterion for testing truth. Researchers from the University of Alabama, Tuscaloosa did just that. They did not intend to talk nonsense, but directly conducted experiments to refute the rumor.

How to conduct an experiment?

The experimental method used by scientists is to use the total absorption method to determine the metabolizable energy of a certain food.

The metabolic products produced during the life activities of animals, except for body heat, gas, trace secretions and epidermal exfoliation, the rest will be excreted through feces and urine. Therefore, by measuring the body heat generated by animals under closed conditions and collecting urine and feces, we can roughly calculate the heat generated by the food, and the heat that is finally digested is called metabolic energy.

Metabolic energy calculation formula (Image source: Animal Nutrition Experimental Tutorial)

Among the rumored negative calorie foods, celery is the most famous. Because most people think celery tastes rough, they think celery is rich in fiber and can burn calories...

Negative calorie food widely circulated on the Internet: celery (Image source: screenshot of a search website)

Is it a negative calorie food? The bearded dragon has the final say

Well, since everyone thinks so, the researchers will satisfy everyone and choose celery as the experimental material, and the experimental subjects are 9 Chow bear lizards.

Chow bear lizard (Image source: Wikipedia)

The researchers chose this strange-looking reptile because they are naturally omnivorous, have a digestive system similar to that of omnivorous mammals, and are docile and willing to eat celery, making them easy to study in the lab.

Since it is a digestion experiment, pretreatment must be done first. First, the lizards were kept in cages and fasted for 10 days to ensure that they would not produce feces related to other foods. Of course, this was not enough, and the researchers also gave them enemas, which cleared out any residual feces or urine that might cause interference.

After these pretreatments, the researchers took the bearded lizard to the metabolic cage for the experiment. The metabolic cage is small and can just fit a bearded lizard. It is mainly used to collect the urine and feces naturally excreted by the experimental animal in order to calculate its overall metabolism. The urine and feces will be collected separately, and the calories of urine and feces can be calculated separately, which can reduce the calculation error.

Desert wood rat in a metabolic cage (Image source: www.eurekalert.org)

The enclosed space controlled the flow of air in and out, allowing the researchers to accurately measure how much energy the bearded dragon consumed by eating the celery in a given period of time.

After entering the metabolic cage, the bearded lizards began to eat, and each lizard could eat 7.83±0.23 kilojoules of celery. Over the next three days, the researchers began to collect their urine and feces every day, and the feces samples were dried and then weighed.

Next, the samples were placed in a bomb calorimeter to accurately calculate the amount of heat produced by the lizards' feces and urine. Finally, after they were done, they were given an enema to ensure that there was no residual celery left in their bodies.

After collecting the experimental data, the researchers began to calculate whether the celery meal produced negative calories (the following is the average data for each lizard):

(Image source: Reference 1)

From the data table we can see that 2.29 kJ are the calories from feces, 1.06 kJ are the calories from urine, 2.53 kJ are the calories produced by digestion, and 1.89 kJ are the net energy intake. The final calculated metabolic energy of celery is 23.4%.

In short, this result shows that celery is not a negative calorie food. 7.83 kilojoules of celery were finally consumed by the bearded dragon as 1.89 kilojoules of calories. Although this was not an experiment with humans as subjects, and this calculation result is not applicable to humans, the researchers said: "If humans eat this celery, they will only consume higher calories."

Can eating more celery help you lose weight? Yes, but it's not realistic

Of course, if you plan to eat celery all the time, you can also lose weight.

Although every bite of celery eaten by these bearded dragons brings in calories, their total calorie intake during these three days is negative. This is because over the three days, the lizards' basal metabolism (the minimum energy metabolism required to maintain basic life activities such as heartbeat and breathing, called basal metabolism (BM)) will eventually exceed the total calories consumed by the celery, losing at least 6 kilojoules of calories.

If a Chow Chow lizard only eats celery for 3 days, it will lose 6 kilojoules of calories, while a female human will lose 4023 kilojoules of calories (Image source: Reference 1)

That is to say, if you plan to live on only a small plate of celery every day, you will most likely starve to death, but as long as you eat enough, the total calorie intake can still meet the daily calorie needs of the human body, provided that you can eat so much celery. Because of this, Chow Chow lizards usually eat more than celery, but also eat higher-calorie foods such as kale, mustard greens, carrots, pumpkin and protein-rich crickets.

At this point, we can say that the final conclusion of this experiment is: celery is not a negative calorie food.

Here is another episode: The son of the scientist who conducted this experiment once proposed to conduct a human experiment on negative calories and wanted to be a volunteer for the experiment. But when he heard that his feces needed to be collected and dried, he decisively refused.