I’m known for telling my clients, “If you have teeth and a small intestine, let your body do the digestion.” Tough love? Maybe not. I typically don’t advise smoothies or juices when you’re looking for weight loss.
Chewing your food well is a habit that’s been advised for many years. Chewing several times not only slows down eating, but also increases the caloric expense linked with the metabolism of food.
Chewing increases intestinal movement, adding up to more heat generation in the body following food intake, known as diet-induced thermogenesis or DIT. But how long you have to chew to see a bump in DIT in the body is unknown.
Dr. Yuka Hamada and Professor Naoyuki Hyashi from Waseda University in Japan published a research study showing a cause-and-effect association between chewing and DIT. It’s available in the journal Scientific Reports.
DIT, also known as the thermic effect of food, raises calorie use above the level of basal fasting and is known to prevent weight gain. Previously, Hamada’s team discovered that slow eating and chewing more slowly increased DIT but also improved blood circulation to the splanchic area of the abdomen -- the section that manages the stomach, small intestine, large intestine, pancreas, spleen, and liver.
Despite the studies linking chewing-induced DIT with improved digestion and absorption in the abdomen, Hayashi sought to find out whether the bolus size of the food that entered the digestive tract added to the rise in DIT seen following slow eating. In addition, do oral stimuli created with prolonged chewing have a role in increasing DIT? His team needed to explore these aspects further before defining slow chewing as an effective and scientific strategy for weight management.
The scientists designed the DIT study to exclude the impact of food bolus by including liquid food. The study included three trials performed on different days. Volunteers were asked to swallow 20 ml of liquid test food normally every 30 seconds for the control trial. The second trial involved having volunteers keep the same test food in their mouth for 30 seconds without chewing, which allowed prolonged tasting prior to swallowing.
Finally, the impact of chewing and tasting were evaluated. The volunteers chewed the 20 ml test food for half a minute at the interval of once per second, then swallowed it. Factors such as hunger and fullness, gas-exchange variables, DIT, and splanchic circulation were then measured before and after the consumption of the test-drink.
The conclusions of Hyashi’s study were quite interesting.
No difference in hunger or fullness scores were seen among the trials. Hayashi notes, "We found DIT or energy production increased after consuming a meal, and it increased with the duration of each taste stimulation and the duration of chewing. This means irrespective of the influence of the food bolus, oral stimuli, corresponding to the duration of tasting food in the mouth and the duration of chewing, increased DIT."
Protein oxidation and gas exchange were also higher with the duration of taste stimulation and chewing, as was blood flow in the splanchic iliac artery. Since this artery brings blood to the digestive system's organs, movement of the upper gastrointestinal tract also increased in response to the oral stimuli of chewing.
Hyashi’s research indicates that chewing food well increases energy expense and may help prevent obesity and metabolic syndrome. He notes, "While the difference in energy expenditure per meal is small, the cumulative effect gathered during multiple meals, taken over every day and 365 days a year, is substantial."
Slow eating and more thorough chewing could be the next suggestions to add to our weight control efforts.
Here are some tips to give your clients that are trying to manage their weight:
- Chews to CHEW food! Limit liquid calories, particularly empty calories from alcohol, sweetened beverages, and sports drinks.
- Count your bites. Chew eat bite of food 30 times before swallowing. Savor the flavors.
- Put your fork down between bites to slow down eating.
- Take a sip of water between bites to get more fluid in between food.
- Practice mindful eating. Think of the how, what, where, and why of what you’re eating.
- Make a layered parfait of yogurt and fruit instead of a fruit smoothie.
- Play with your food (in your mouth). Swish it around and hit all those glorious taste buds.
- Pick foods that force you to chew like chunky instead of smooth peanut butter and fresh fruit instead of canned fruit or juice.
By Lisa Andrews, MEd, RD, LD
- Yuka Hamada, Naoyuki Hayashi. Chewing increases postprandial diet-induced thermogenesis. Scientific Reports, 2021; 11 (1) DOI: 10.1038/s41598-021-03109-x
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.