That chewing food well makes a healthy eating habit is an age-old wisdom. Eating slowly and chewing thoroughly helps prevent obesity and weight gain — a view popularized a century ago and then tested in sporadic scientific studies. Typically, the chewing process is said to increase the energy expenditure associated with the metabolism of food and increase gut motility – all summing up to an increased heat build-up in the body after food ingestion, known as diet-induced thermogenesis (DIT). However, how prolonged chewing induces DIT in the body remains unclear. Recently, Dr. Yuka Hamada and Professor Naoyuki Hayashi of Waseda University, Japan, published a study that establishes a causal link between chewing and DIT.
DIT, also known as the thermic effect of food consumption, increases energy expenditure above the basal fasting level – a factor known to prevent weight gain. Previously, the team found that eating slowly and chewing thoroughly not only increased DIT, but also improved blood circulation in the splanchnic area of the abdomen. While these studies associated chewing-induced DIT with increased digestive and absorption-related activity in the abdomen, they left room for further exploration of a few crucial points. Hayashi explains:“We were unsure whether the size of the food bolus entering the digestive tract contributed to the increase in DIT seen after slow eating. Do oral stimuli generated during prolonged food chewing also play a role in increasing DIT? To define slow chewing as an effective and scientific weight management strategy, we had to look deeper into these aspects.”
To find the answers, the researchers designed their new study to rule out the effect of the food bolus by using liquid foods. The entire study involved three trials conducted on different days. In the control trial, they asked the volunteers to normally swallow 20 ml of liquid test food every 30 seconds. In the second trial, the volunteers held the same test food in their mouths for 30 seconds without chewing, giving them a long taste before swallowing. Finally, in the third trial, they studied the effect of both chewing and tasting; the volunteers chewed the 20 ml test food for 30 seconds at a frequency of once per second and then swallowed it. The variables such as hunger and fullness, gas exchange variables, DIT and splanchnic circulation were duly measured before and after the consumption of the test drink.
The results of this well-designed study were quite insightful. There was no difference in hunger and fullness scores between the trials. However, as Hayashi describes:“We found that 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, regardless of the influence of the food bolus, oral stimuli corresponding to the duration of food tasting in the mouth and duration of chewing increased DIT.” Gas exchange and protein oxidation also increased with duration of taste stimulation and chewing, and so did blood flow in splanchnic celiac disease. Since this artery supplies blood to the digestive organs, the motility of the upper GI tract also increased when responding to oral stimuli during chewing.
The study highlighted that chewing well, by increasing energy expenditure, can indeed help prevent obesity and metabolic syndrome. Hayashi concludes, “While the difference in energy expenditure per meal is small, the cumulative effect accumulated over multiple meals taken every day and 365 days a year is significant.”
Backed by robust science, eating slowly and chewing thoroughly could be the latest recommendations for integration into our weight management efforts.
