Study Spotlight Take-Away with Chef Dr. Mike: Chews Wisely

by Michael S. Fenster, MD

If you truly get in touch with a piece of carrot, you get in touch with the soil, the rain, the sunshine. You get in touch with Mother Earth and eating in such a way, you feel in touch with true life, your roots, and that is meditation. If we chew every morsel of our food in that way, we become grateful and when you are grateful, you are happy.”

Thich Nhat Hanh

Mindful eating techniques and food-based gratitude exercises, such as those described by the renowned Vietnamese Zen Buddhist monk Thich Nhat Hanh, can be found in many spiritual practices across the globe. This connection between the food we eat and human spirituality extends backward in time to the forebears of our Homo sapiens sapiens ancestors, who first appeared roughly 300,000 years ago. Both the Neanderthals (Homo neanderthalensis), who existed as far back as 400,000 years ago, and Homo naledi, who lived as far back as 335,000 years ago, displayed possible intentional burial practices that included placing valuable food items alongside their dead. This month, in a few short weeks, many of us will enjoy the annual autumn celebration of Halloween. This originates in the ancient Celtic Festival of Samhain, which focused on the supernatural and death. In our modern version, we replace the carved beets, turnips, and other humble – but natural – food offerings with a big sack of ultra-processed sweeties.

This week’s Study Spotlight focuses on a small but important study that lightly touches on this tradition in a timely manner. Small in the sense that the study only observes nine overweight/obese Japanese men. Important in the sense that, in many ways, it confirms the findings of Kevin Hall’s earlier seminal study. In Hall’s previous work, a group of 20 participants consumed two diets for two weeks in which the only difference was the ultra-processing. During the consumption of ultra-processed foods (UPFs), the participants gained approximately 1 kg, which they lost when they stopped eating the UPFs[1].

The Study:

  • The study examined nine overweight/obese, otherwise healthy Japanese men.
  • The mean age was 29.7 years, and the mean body mass index (BMI) was 27.4 kg/m2.
  • During the study, the participants were assigned to either a UPF-based diet or a non-UPF-based diet for one week, followed by a two-week washout period, after which they switched to the alternate diet for an additional week.
  • Meals were matched for total energy and macronutrient levels, and participants were allowed to eat as much as they wanted within a 60-minute time limit per meal three times per day.
  • Participants also had access to snacks and bottled water throughout the day, which were designed to match total energy and macronutrient levels across diets.
  • Non-UPFs were defined as NOVA groups 1-3, whereas UPFs were defined as NOVA group 4 classification.
  • The primary outcome was the difference in body weight change during the UPF and non-UPF periods.
  • The secondary outcomes were the differences in the average daily energy intake, changes in body composition, intake of each macronutrient, the eating rate (i.e., the number of calories consumed per minute and the grams per minute), chewing frequency (i.e., the number of chews per minute and number of chews per gram), the levels of lipid profiles, liver function variables, appetite-related hormones and the VAS ratings for appetite during each diet period.

The Caveat:

The participants gained an additional 1.1 kg in weight during the period of consuming UPFs compared to when they consumed non-UPFs, a finding strikingly similar to Hall’s earlier study results. The energy composition of the daily meals and snacks offered were remarkably similar at 5239 kcal per day during the non-UPF period and 5298 kcal per day during the UPF period. There was a similarity in macronutrient (carbohydrate (~53%), fat (~33%), and protein (~14%)) composition between the UPF and non-UPF diets.           

However, the average daily energy intake was statistically significantly higher by 813.5 kcal during the UPF consumption week vs the non-UPF week. The increased energy intake during UPF consumption was attributable to increased carbohydrate (although fiber intake decreased) and fat consumption. These findings suggest that there is something in the manufacture of ultra-processed foods that causes people to eat more of them, a finding that again aligns with Hall’s previous study. Comparing a week of ultra-processed foods versus a week of non-ultra-processed foods, the total weight differential in the present study was over two kilograms (roughly 4.5 pounds). The current study also found that people ate faster and chewed less when consuming ultra-processed foods.

A more granular examination found that when the participants switched to the non-UPF diet, LDL cholesterol significantly decreased compared to baseline. Conversely, the UPF diet was associated with a significant increase in blood triglyceride levels. Unsurprisingly, this was also accompanied by significant increases in liver inflammation; blood levels of the liver enzymes AST, ALT, and γGTP were all elevated after a week of eating ultra-processed foods.

The study’s small sample size of nine participants and inclusion of only overweight/obese Japanese men limit the generalizability of the findings. Also, the short duration of the diet periods does not allow for an assessment of the long-term effects of UPF consumption.

However, the results of the study, taken together with the results of Hall’s prior study, suggest that there is something beyond macronutrient composition and caloric value that is inherently detrimental to engaging in the large-scale consumption of ultra-processed foods. This study explores potential etiologies that include ultra-processed foods (generally more energy-dense than non-ultra-processed foods) designed to be chewed less and eaten faster. This fact was first brought to light by Dr. David Kessler in his book, The End of Overeating: Taking Control of the Insatiable American Appetite[2], which explored the industrial food processing industry.

The mechanisms by which chewing keeps us slimmer may involve nerve stimulation from chewing that acts at the satiety center in our brain to help prevent us from overeating. Increased chewing, for example, chewing 40 times before swallowing a fixed amount of food as opposed to 15 times, results in elevated postprandial release of GLP-1, a glucose-dependent insulinotropic peptide that current weight loss drugs like Wegovy act to mimic, and cholecystokinin; as well as a tendency towards suppression of the postprandial release of ghrelin (the hormone that makes us hungry).

So, this holiday season, chews wisely and exercise those ultra-processed demons away!


The Study:

Hamano S, Sawada M, Aihara M, et al. Ultra-processed foods cause weight gain and increased energy intake associated with reduced chewing frequency: A randomized, open-label, crossover study. Diabetes Obes Metab. 2024; 26(11): 5431-5443. doi:10.1111/dom.15922.


Additional resources:

Fukuda H, Saito T, Mizuta M, et al. Chewing number is related to incremental increases in body weight from 20 years of age in Japanese middle-aged adults. Gerodontology. 2013;30(3):214-219. doi:10.1111/j.1741-2358.2012.00666.x

Hall, Kevin D.; (2019). Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metabolism. 2019. 30(1): 67-77. https://doi.org/10.1016/j.cmet.2019.05.008   

Kessler, David A. The End of Overeating: Taking Control of the Insatiable American Appetite. (2009). Rodale Books.

Krop EM, Hetherington MM, Nekitsing C, Miquel S, Postelnicu L, Sarkar A. Influence of oral processing on appetite and food intake – a systematic review and meta-analysis. Appetite. 2018;125:253-269. doi:10.1016/j.appet.2018.01.018

Li J, Zhang N, Hu L, et al. Improvement in chewing activity reduces energy intake in one meal and modulates plasma gut hormone concentrations in obese and lean young Chinese men. Am J Clin Nutr.2011;94(3):709-716. doi:10.3945/ajcn.111.015164

Takahara M, Fukuda M, Matsuzawa Y, Shimomura I. Effect of tasteless calorie-free gum chewing before meal on postprandial plasma glucose, insulin, glucagon, and gastrointestinal hormones in Japanese men without diagnosed glucose metabolism disorder: a pilot randomized crossover trial. Diabetol Int. 2020;11(4):394-402. doi:10.1007/s13340-020-00435-9

Uehara F, Hori K, Hasegawa Y, et al. Impact of masticatory behaviors measured with wearable device on metabolic syndrome: cross-sectional study. JMIR Mhealth Uhealth. 2022;10(3):e30789. doi:10.2196/30789.

Zhu Y, Hollis JH. Relationship between chewing behavior and body weight status in fully dentate healthy adults. Int J Food Sci Nutr. 2015; 66(2):135-139. doi:10.3109/09637486.2014.979317.

[1] (Hall, 2019)

[2] (Kessler, 2009)

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