I grew up in a house with eight family members, and though my parents produced a mountain of food to keep us fed there was always a rush at dinnertime. The first to finish were the ones to get seconds, and we all wanted seconds. As an athlete my caloric needs were astronomical, but even during periods of relative inactivity I had an overwhelming need to eat and eat. I got tired of this drive to eat and would skip meals, only to find myself shoveling mac and cheese or mashed potatoes like I'd been rescued from a deserted island.
Not surprisingly, I have always struggled with my weight and appearance, and it turns out there is a direct relationship between weight gain and eating speed that has nothing to do with willpower. Without evidence, the general consensus about chew-speed and weight gain is considered a consequence of calorie intake, but the calorie model of weight loss is total bullshit (just ask any of millions of failed and frustrated dieters). Many lean people can eat huge amounts of calories and not gain weight. For my own experience, reducing calorie intake didn't make me lean but contributed to metabolic failure and thyroid cancer. And yet most healthy people who are lean do chew more slowly and eat less calories. So what is going on?
BACTERIA AND BLOATING
Most people assume that anything they eat is dissolved by stomach acid. This isn't entirely true. Acid breaks up food but it doesn't reduce molecules the way enzymes do. When undigested food enters into the intestinal system it is acted upon by bacteria. The fermentation of carbohydrates and produce an explosion in bacterial growth and thus bacterial metabolic byproducts, called exotoxin and endotoxin, which then overload the body's detoxification process in susceptible individuals. These bacterial byproducts lower the metabolic rate and slow cellular functions, over time it contributes to and causes bloating, fatigue, and metabolic disease. Mostly, the endotoxin absorbed into the body stimulates fat deposition. This effect is also why fast eaters are hungrier and eat more food—we eat to feed bacteria, and the bacteria stimulate storage of calories rather than their consumption for energy, but we still have to feed the rest of our body on top of that. Strange as it may sound, this is not really a mistake or error of biology. We have evolved a symbiotic relationship with these bacteria, and they are an integral part of our body's methods for a variety of biological functions, including this aesthetically undesirable one, the effect of which is to protect us against starvation and infection.
If an organism is stressed or panicked it would make sense that their body should store more calories. Stressed people eat quickly. We only chew enough to swallow before moving on to the next bite. This is not, as often characterized, a defect or lack of willpower. It is a biological response allowing animals such as ourselves to survive. But our human ancestors experienced serious stress only during times of famine. In our modern, cramped and self-centered societies we live with constant stress, and those of us who are susceptible to it respond to our biological programming to panic eat. It appears to the ignorant and asinine that fast eaters eat more calories and so gain more weight, but the cause is not calories. It is the bacterial endotoxin stimulating calorie storage.
SLOW CHEWING AND SALIVA
Those who chew slowly are lean because of important enzymes in the saliva, not because of reduced calorie intake. When slow-eating, these enzymes have time to digest the food before it reaches intestinal bacteria, thus preventing fermentation. Salivary amylase is an enzyme which breaks down carbohydrates, most importantly starch, into simpler sugars which are quickly absorbed into the body. It is only located in the mouth and differs chemically from pancreatic and other amylases. When starches are well-saturated with saliva they break down before they can be consumed by bacteria, thus reducing bacteria overload, endotoxin exposure, and weight gain. This also has the effect of fueling your body immediately, giving you energy from the food right away. Stressed people have lower levels of amylase in their saliva, so it's even more important for those with health problems to take their time when eating. Salivary amylase works best on non-grain carbohydrates (vegetables, fruit, tubers) and has less of an effect on grains, so avoiding grain would be important for weight loss or digestive issues. But even if you insist on enjoying grains you can still reduce negative impacts on your health by waiting until each bite is thoroughly wet with saliva before swallowing.
OTHER HEALTH BENEFITS
When I began consciously chewing my food I thought I would get tired from chewing that much food. But to my surprise, and relief, I found I got full very quickly and didn't even want to eat as much as I have been accustomed (it's not about chewing exactly, so chew leisurely and give your food time to react to the enzymes in the saliva). Meals are more enjoyable, I'm satiated quickly, and instead of being full and lethargic I am light and energized. It only takes about 48 hours of eating this way for intestinal discomfort to subside (and this should be a guide for if you are doing it right. If discomfort persists and you're still eating grains then those should be cut out until you are well). I've been easily losing unwanted body fat without exercise, sleeping better, and feeling happier. The reduction in endotoxin has eliminated all bloating or stomach discomfort, and since endotoxin contributes to so many other metabolic problems, significant healing of other health problems can occur just from chewing food thoroughly. Of course, a diet of good fats and plenty protein and carbohydrates is also important when it comes to maintaining health and appearance, and more on that can be read in my article The Truth About Fat, or you can supercharge your weight-loss efforts by How To Do A Low-Fat Diet.