Statistics from early 2019 show the US obesity rate approaching 40 percent after holding steady around 35 percent a decade earlier. These numbers are even more startling when you consider it was only 20 years ago that no state had an adult obesity rate greater than 15 percent.
What’s behind this trend? Most authorities point to diet rather than lifestyle. We just eat too much, more calories than we use. And the excess are stored for the future. Our weight sneaks up.
How does our diet differ from past generations? The most likely explanation is a shift in the ratio of plant to animal protein.
Man has been an omnivore (eating both animals and plants) for at least a million years. A unique bone disease associated with vitamin B12 deficiency (a vitamin found only in animal meat and dairy products) is proof that man has always needed some animal protein in his diet.
But analysis of fossilized feces (paleopoop) suggests that meat was a rare treat in a diet containing more than 100 grams of plant fiber a day.
With plants the primary source of nutrition, it has been speculated that it was the fiber in our ancestor’s diet that sent the signal we had eaten enough. Dietary fiber is metabolized in the colon into short chain fatty acids (SCFA). These SCFAs in turn can affect multiple metabolic pathways so it is not unreasonable to conclude they might provide the satiety signal. Eat less fiber, fewer SCFAs are produced, and we remain on the hunt for more food. So it may be the absence of adequate fiber in our diet that is the trigger to keep pouring in the calories.
Now let’s jump ahead a million years to one of the biggest changes in man’s diet over the last 50 years - the explosive increase in processed foods.
Strictly speaking, a processed food is any grocery item that has been modified from its original form. But processing covers much more than just mechanical alteration and can include the removal of fiber as well as fortification with additional fats as well as sugar and salt.
Why pick on processed foods?
Twenty people, in a month long controlled study, ate an unlimited diet of highly processed foods for two weeks and then switched to unprocessed or minimally processed foods for a second two weeks. On a processed diet they ate an average of 500 more calories per day and gained an average of two pounds over the two weeks. Then on an unprocessed diet lost an average of two pounds.
There are several possible explanations.
On processed foods, subjects ate nearly 50 calories per minute but only 32 calories per minute on unprocessed foods. Eating processed foods means you can eat more calories before your stomach signals your brain you are full. It takes far more time to chew up unprocessed foods before you swallow them, and eating more slowly usually means you eat less.
Another possibility is the form and size of the food particles. Carbohydrates, fats and proteins all must be reduced to simpler single sugars, amino acids, and fatty acids before they can be absorbed into the blood stream.
Processing reduces the size of food particles and makes further digestion that much easier. This in turn increases the calories you absorb from that food. Grinding whole grains into flour or cooking starchy vegetables increases the number of calories you absorb from those foods.
Cooking itself modifies foods and increases absorption. Boiling, baking or frying modifies starches, markedly increasing the calories you will absorb from root vegetables such as potatoes, turnips, cassava, yams, and rutabagas.
One has to consider energy density. Even before digestion the added sugar and oils increase the calories per ounce in processed food. The same portion size contains more calories.
And finally there is the fiber argument. Less fiber for the microbiome and fewer SCFAs for the satiety feedback loop. Not to mention that processed foods contain emulsifiers as a way to prolong shelf life and keep ingredients from separating. In mice emulsifiers disrupt intestinal bacteria (the microbiome) resulting in weight gain. If these same changes occur in the human colon, emulsifiers may be another piece of the weight gain explanation as they mean any fiber reaching the colon could be less effective in SCFA production.
What does this all mean for weight management? A few simple changes in your diet, a few less calories per day, can pay big rewards over time.
Eat fewer processed foods. Change your route through the store. Ultra - processed foods lurk in the center aisles. Walk the perimeter with its fresh fruits and vegetables first and go down the aisles only when you have a specific item in mind.
Add more fresh fruits and vegetables to your diet. Especially fruits and vegetables that are not cooked, ground or softened. They are great as a snack alternative.
And eat more whole grains, beans, seeds and nuts that have not been ground into flour. This includes fewer foods made from flour such as bakery products and pastas.
It will take some planning, but using what you know about fiber provides an opportunity to quit counting calories.
References:
https://www.ama-assn.org/delivering-care/public-health/adult-obesity-rates-rise-6-states-exceed-35-7
