What do whole fruits, fatty desserts, and a nagging mother have in common? These are some of the secrets to eating the foods you want to or thought you could never get away with eating, while still looking and feeling great. The speed at which your food is digested impacts its physiological effects on your body. We all know the difference in how you feel if you chug a milkshake as fast as you can compared to sipping at it, or the meaning of “food that goes right through you.” The speed of digestion can actually impact your hormones that control fat gain and loss. This is good to know if you’re interested in losing weight or maintaining fat loss.
So how is it that speed of digestion impacts body weight? The faster a large amount of glucose gets dumped into your system, the larger the insulin response. Although the exact mechanism of how this increases weight gain is still being debated, some of the best research suggests that an excess insulin response influences leptin, an incredibly important hormone that has a hand in regulating everything from satiety and hunger to your sleep schedule. Leptin resistance, which is thought to be a major contributor to the development of obesity, is probably driven by excess insulin which is provoked through ingesting large amounts of sugar or protein without mechanisms to slow their absorption. The takeaway is this: the slower food enters and moves through your system, the more appropriate your hormonal response will be, which decrease your chance of accumulating excess fat.
It’s common knowledge that fiber can speed up your digestion if constipation is a problem. Interestingly enough it can also slow down your digestion, specifically of sugars. This is the reason that whole fruit does not raise your blood sugar and insulin nearly as high as fruit juice, which contains only a small fraction of the fiber found in its equivalent whole fruit, if any. In addition the increased water content of whole fruits, whole vegetables and unprocessed meat may also have an impact on slowing down digestion, by slightly diluting the acids and enzymes that break down your food for energy. This leads to an important rule: whole food > processed food, and so by extension, whole fruit > fruit juice.
Another useful, although less commonly discussed phenomenon is the effect of a meal’s fat content on gastric emptying – in other words the higher the quantity of fat in food, the slower the stomach empties into the intestine (modulated by cholecystokinin or CCK for short). This slowed emptying results in slower digestion of sugars and protein which in turn lessens the response from insulin, and therefore has a smaller impact on leptin. If the fat content of a meal is high enough, then the resulting glucose load will be spread over a longer period of time. This will decrease its effect on insulin and therefore on fat accumulation. In practice, many people find that they can eat high-fat desserts like ice cream a few days a week without negatively impacting their body weight.
Here is where your nagging mom comes into play. Did she ever yell at you to chew your food? Her advice can help you to lose weight or stay trim. An additional effect of the fiber in veggies and eating protein in the form of whole meat is to increase the time needed to mechanically break down food through mastication (chewing). If the food is physically harder to break down it will take longer to eat a certain quantity of food (think apples versus applesauce). Further down the digestive tract, the result will again be to blunt the glucose load on your system which, as we have seen, may affect fat gain. Another way you can slow down at meal time is to eat with friends and family. Taking breaks to talk and laugh and enjoy the experience of good food with good company will not only help to make the meal more enjoyable, it may even make it more health promoting.
Chew slowly, talk often, butter your veggies, and be thin.