How Chewing (Gum/Food) Affects Your Energy Expenditure: Gum + Slow Eating Triple 3h Diet Induced Thermogenesis

If chewing gums can help triple the diet-induced thermogenesis. Does this mean that your doctor will soon prescribe chewing gums instead of diet and exercise or even weight loss surgery?
Slow eating, which involves chewing food slowly and thoroughly, is - according to most research, at least - an effective strategy for controlling hunger level and energy intake in overweight or obesity (Andrade. 2008; Smit. 2011). And the fact that slow eating / chewing more frequently aids weight management even in the people who don't tend to overeat, may - as a recent study from the Tokyo Institute of Technology shows - be a consequence of more than just a reduction in energy intake.

As Hamada et al. show in two recent studies in Obesity, eating slowly will also ramp up the postprandial energy expenditure and fat oxidation aka the "diet-induced thermogenesis" (DIT) of healthy, normal-weight men and women without one of the pertinent eating disorders.
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From their previous research, the authors knew that "increasing DIT by slowing the eating speed can be difficult for individuals to accomplish, since the natural eating speed is acquired over a long period of time" (Hamada. 2016). In the latest follow up, the scientists sought to investigate, whether the postprandial gum chewing increases DIT via an increase in the splanchnic circulation in eleven healthy, normal-weight subjects [7 males and 4 females; age, 24 ± 1 years (mean ± SD); height, 164 ± 10 cm; weight, 56 ± 6 kg; and body fat, 18 ± 8%].
Figure 1: Diagram for outline of study protocol. VAS, measurement of visual analog scale (Hamada. 2016).
As the illustration of the study design in Figure 1 tells you, Hamada et al. chose a randomized crossover design. The subjects completed four trials on four different days, with consecutive trials separated by more than 3 days (see Figure 1).
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"The subjects arrived at the laboratory at 9:00 a.m. after having abstained from eating, consuming caffeinated or alcoholic beverages, and intense exercise since dinner on the previous night (i.e., they had fasted for more than 10 h). Each subject was seated on a chair in a semisupine position in a quiet room in which the temperature and humidity were controlled to within 25.0 +/- 0.48C and 50 +/- 4%, respectively. After allowing the subjects to adjust to the experimental setup for 20 min, baseline data of gas-exchange variables and the splanchnic circulation were recorded while resting for 20 min. The subjects completed a visual analog scale (VAS) questionnaire to assess their hunger before the test meal.
After the previously described baseline data measurements, the subjects chewed the 621-kcal test meal for as long as possible and as many times as possible in the slow-eating trials, while they consumed the same meal as rapidly as possible in the rapid-eating trials (details from Hamada. 2016):
  • In the gum-chewing trials, they started chewing 1.5 g (3 kcal) of sugarless gum with a lime-mint flavor (Lotte, Japan) immediately after the meal and chewed this gum at a natural pace for 15 min. 
  • In the non-gum-chewing control trials, they consumed 3 kcal of sugar with the meal instead of chewing the gum. 
  • In each rapid-eating and slow-eating trial, they were instructed to eat the meal at a similar speed in the non-gum-chewing and gum-chewing trials. Gasexchange variables and the splanchnic circulation were recorded until 180 min after the meal (note: I am not going to discuss this data in detail, but if the scientists are right the increase in the amount of blood that's circulating in the organs of the splachnic bed, is more than a correlate of the increase in energy expenditure).
The four trials of combinations of rapid eating and non-gum chewing, rapid eating and gum chewing, slow eating and non-gum chewing, and slow eating and gum chewing were labeled as RN, RG, SN, and SG, respectively.
The test meal (photos are not from the study, but show the products that are listed in the methods section) had a macro composition of 13% protein, 28% fat, and 59% carbohydrate and was spaghetti carbonara with orange juice and a regular yogurt.
What was the test meal? Test meal The 621-kcal test meal (energy proportions: 13% protein, 28% fat, and 59% carbohydrate) consisted of carbonara spaghetti (452 kcal; Nippon Flour Mills, Japan), yogurt (59 kcal; Meiji, Japan), and orange juice (110 kcal; Kirin Beverage, Japan). The temperature of the meal was measured using an infrared thermometer (A&D, Japan), and the meal was provided at a controlled temperature (spaghetti, 58 +/- 1*C; yogurt, 7 +/- 1°C; orange juice, 7 +/- 1°C | You're wondering about the temperatures? Well, we know that cold food has a thermogenic effect. Accordingly, you have to tightly control the food temperature to avoid temperature differences to mess with your results.).
To make sure the number of chews was measured accurately, the scientists went so far to determine the number from a videotape recording of the subject’s face and from recordings of the electromyographic (EMG) activities of the chewing muscles obtained using a standard electrocardiograph (MEG-2100, Nihon Kohden, Japan).
"The chewing duration of the meal was assessed as the duration from the first bite to swallowing after the last bite of the meal. The number of chews was counted using a hand tally counter while watching the videotape recording. The obtained numbers were double-checked using the EMG recordings. The chewing duration and the number of chews were measured twice. There was a small difference (less than 2.8%) between the measurements, and so they were averaged. The total chewing duration and the total number of chews were defined as the summed data obtained during the periods of meal and gum chewing" (Hamada. 2016).
The accurate measurement of the eating speed and chewing frequency, along with the rigid control of hunger, when the subjects arrived at the lab (pre-hunger values did not differ), and the sophisticated analysis of the gas-exchange variables and DIT, are certainly strengths of the study at hand - a study, the results of which confirmed the researchers expectations: the diet induced thermogenesis (DIT) was significantly greater in the gum-chewing trials than in the non-gum-chewing trials for both rapid-eating and slow-eating trials.
Figure 2: Time courses of changes in gas-exchange variables and DIT in rapid-eating trials (RN vs. RG, left panels) and slow-eating trials (SN vs. SG, right panels). Hatched bars indicate the duration of gum chewing. Filled and open circles denote data for the non-gum-chewing and gum-chewing trials, respectively. VO _ 2, oxygen uptake; *P < 0.05, vs. resting baseline in each trial. # P < 0.05, difference between trials (Hamada. 2016).
Even though these results are good news for chewing gum producers, the revelation that the difference in DIT between rapid-eating and slow-eating trials was greater than that between non-gum-chewing and gum-chewing (compare left vs. right graphs in Figure 2) suggests that only a combination of both: slow eating (high number of chews) and post-meal chewing gum will maximize the thermogenic effect of (low protein) meals.
To chew or not to chew, that is not the question! While it appears to be out of question that deliberately chewing more thoroughly and thus eating slower will increase your respiratory exchange ratio (RER, a marker of fat oxidation) and diet induced thermogenesis (DIT) compared to bolting your food (compare left hand vs. right hand graphs in Figure 2), the important question we still have to answer is: How practically relevant is this statistically significant difference?

Figure 3: Diet-induced thermogenesis (DIT) and postprandial splanchnic blood flow (BF) accumulated over the 180-min period immediately after the meal. Filled and open bars indicate data for non-gum-chewing and gum-chewing trials, respectively. *P < 0.05, non-gum-chewing vs. gum-chewing trials. #P < 0.05, rapid-eating vs. slow-eating trials (Hamada. 2016).
To answer this question, we need the data in Figure 3, data which reveals that the difference between eating rapidly and chewing no gum, on the one, and eating slowly and chewing gum, on the other hand, is 350 cal/kg over 3h. That sounds huge, but only if you are not looking at the units closely. Since we're talking about calories, not kilocalories, the average 80 kg man would burn less than 30 kcal extra - that's bull? Well, that's about the same increase in DIT you can expect from a high protein vs. high carbohydrate meal if you extrapolate the data from a 2002 study by Carol Johnston et al. - an effect of which future studies must determine whether it adds to the effect of chewing more thoroughly and using a gum after your meals | Comment!
  • Andrade, Ana M., Geoffrey W. Greene, and Kathleen J. Melanson. "Eating slowly led to decreases in energy intake within meals in healthy women." Journal of the American Dietetic Association 108.7 (2008): 1186-1191.
  • Hamada, Yuka, Hideaki Kashima, and Naoyuki Hayashi. "The number of chews and meal duration affect diet‐induced thermogenesis and splanchnic circulation." Obesity 22.5 (2014): E62-E69.
  • Hamada, Yuka, Akane Miyaji, and Naoyuki Hayashi. "Effect of postprandial gum chewing on diet‐induced thermogenesis." Obesity (2016).
  • Johnston, Carol S., Carol S. Day, and Pamela D. Swan. "Postprandial thermogenesis is increased 100% on a high-protein, low-fat diet versus a high-carbohydrate, low-fat diet in healthy, young women." Journal of the American College of Nutrition 21.1 (2002): 55-61.
  • Smit, Hendrik Jan, et al. "Does prolonged chewing reduce food intake? Fletcherism revisited." Appetite 57.1 (2011): 295-298.
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