Your mother was right: It’s important to chew your food thoroughly before swallowing it. Chewing is the first step in the digestion of the food we eat – it breaks down food into smaller particles, which increases the surface area so that digestive enzymes can more readily extract the nutrients from it. If we rush through our meals, we don't get the full phytochemical benefit of the foods we're eating. Slowing down and chewing thoroughly allows us to absorb more nutrients, helps us maintain a healthy weight, and even brings dental health benefits.
Summary
The digestive process begins in your mouth as soon as you start chewing. When you break your food down into smaller particles, the digestive enzymes can cover a larger surface area and start to extract the nutrients. For some foods, particularly cruciferous and Allium vegetables, breaking down the structure of the food matrix drives chemical reactions that provide beneficial phytochemicals.
Related:
The cancer-fighting power of cruciferous vegetables
How garlic and onions promote cardiovascular health
Eat healthfully, and abundantly, for weight loss
The carotenoids in raw carrots are made more accessible when the plant cell walls are ruptured by thorough chewing. Carotenoids are embedded in the matrix of the food, and the structure needs to be broken down to allow the digestive system to extract and absorb them.1,2 For some foods – specifically cruciferous vegetables and onion and garlic family members – breaking down the structure of the food matrix drives chemical reactions that produce beneficial phytochemicals.
Glucosinolates in cruciferous vegetables (such as broccoli, cauliflower, kale, collards, and bok choy) are converted by the enzyme myrosinase into breakdown products including indole-3-carbinol and isothiocyanates (ITCs), which are compounds with beneficial anti-cancer activity. The extent of formation of ITCs depends on a number of factors, such as the food’s glucosinolate content, temperature, pH, the presence of vitamin C (which accelerates the production of ITCs), and importantly, how much the food is broken down by chopping, crushing, or chewing.
Glucosinolates and myrosinase are physically separated in the intact vegetable, and damage to the cellular structure is necessary to bring them into contact and start the chemical reaction. Heat inactivates myrosinase, and also degrades vitamin C, which slows or stops the reaction. To maximize the health benefits, cruciferous vegetables should be eaten raw or chopped finely before cooking.
Similarly, onions, garlic, leeks, scallions, and shallots contain an enzyme called alliinase that is damaged by heat, and physically separated from the sulfur compounds it metabolizes. Physically disrupting the plant cell structure by chopping or chewing well starts the chemical reaction that produces allicin and other beneficial compounds with antioxidant, anti-inflammatory, and anti-cancer effects.3
Related: How garlic and onions promote cardiovascular health
Chewing thoroughly also enhances the conversion of dietary nitrate to nitric oxide by oral bacteria. The body needs nitric oxide a variety of functions, including cell signaling and blood pressure regulation. One of the two major sources of nitric oxide is dietary nitrate, which is converted to nitric oxide by oral bacteria on the surface of the tongue. Green vegetables are the richest sources of nitrate, and the production of nitric oxide by oral bacteria increases when we chew more thoroughly. Note that this process only occurs in the presence of oral bacteria.4-6 For example, when we blend cruciferous greens into a smoothie, we will achieve good conversion of glucosinolates to ITCs, but we won’t get as much nitric oxide production in the mouth than if we had chewed the greens instead.
Sources:
Dietary factors that affect the bioavailability of carotenoids
Garlic and onions: their cancer prevention properties
From Nitrate to Nitric Oxide: The Role of Salivary Glands and Oral Bacteria
In addition to extracting more phytochemicals from vegetables, studies suggest that chewing thoroughly and eating more slowly helps maintain a healthy weight. Observational studies have found that participants who reported eating more slowly had lower body weight or gained less weight over time, compared to faster eaters.7,8 In another study, a greater number of chews and longer chewing time were associated with lower body mass index (BMI).9
Chewing more thoroughly may promote a healthy weight by affecting hunger and satiety signals, which could reduce calorie intake in the current meal, and delaying or reducing calorie intake in the next meal. A meta-analysis of studies on chewing time found that participants reported feeling lower levels of hunger after a meal of longer vs shorter chewing time.10
Related: Eat healthfully, and abundantly, for weight loss
Several studies have also found that prolonged chewing reduced calorie intake either at that meal or the next meal.10-12 For example, one study had participants eat as much as they liked of a meal while chewing either 15 or 50 chews per bite, and those who chewed 50 times per bite consumed fewer calories.13 A similar study comparing 15 and 40 chews had similar results.14 A smaller bite size is also linked lower food intake.15
Diet-induced thermogenesis, also called the thermic effect of food, is the energy burned to digest, absorb, and metabolize food. It is a significant contribution to our daily calorie burn, making up as much as 10-15% of the calories we expend in a day.16 There is evidence that chewing more thoroughly increases diet-induced thermogenesis.16,17
Sources:
Faster self-reported speed of eating is related to higher body mass index in a nationwide survey of middle-aged women
Relationship between chewing behavior and body weight status in fully dentate healthy adults
Effects of chewing on appetite, food intake and gut hormones: A systematic review and meta-analysis
Increasing the number of chews before swallowing reduces meal size in normal-weight, overweight, and obese adults.
Chewing increases postprandial diet-induced thermogenesis
Chewing thoroughly stimulates more saliva production, which is a key factor in preventing dental erosion and dental caries (cavities). First, the extra saliva helps remove small food particles and sugars from the teeth. Increasing saliva production helps restore proper pH in the mouth after a meal by diluting and buffering acid; an acidic environment promotes erosion of tooth enamel. Plus, saliva contains minerals, specifically calcium and phosphate, which help to re-mineralize teeth.18
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