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Here's another relatively new take on safe starches for paleo diets. It's not always about feeding you, sometimes it's about feeding your probiotic bacteria.

Even our paleolithic ancestors consumed some starches. Potatoes and grains as we know them now did not exist before 10,000 to 12,000 years ago, but there is good evidence that humans gathered and ate tubers and starchy roots of various plants as long ago as 35,000 years ago. Sugar sabotages modern diets, but starch is not necessarily always a bad thing. Here's why:

  • The brain's preferred fuel is glucose. Even though the brain comprises 2% of the body's total mass, it uses about 20% of the body's glucose supply. Starches break down into glucose without potentially toxic byproducts.
  • Starches break down into glucose, but only slowly, and incompletely. They do not place the same burdne on the body as other carbohydrate foods. 
  • Tubers generally contain "resistant" starches. These complex molecules can't be broken down by enzymes the human body produces, but they can be broken down by probiotic bacteria. They bacteria turn resistant starch into fatty acids such as propionic acid and butyric acid that the body can burn for fuel, but can't store as fat. Most of the energy needs of the colonocytes, the cells lining the colon, are provided by these fatty acids, and as much as 6 to 7% of all the calories your body burns come from fatty acids broken down from resistant starch by bacteria, not by your own digestive enzymes.

The butyric acid that probiotic bacteria make from resistant starch holds a number of benefits for their human hosts. Butyric acid:

  • Prevents degeneration of neurons in the brain. The brain can use butyrate to make energy when other energy sources are deficient. Butyrate prevents the need of creating ketone bodies from other fats, or breaking down protein into glucose and toxic urea.
  • Fosters tissue repair throughout the body. A laboratory study with animals found that supplemental butyrate and vitamin A accelerated tissue repair after experimentally induced heart attack.
  • Heals inflammatory bowel disease. Doctors have successfully used butyrate treatments for Crohn's disease and ulcerative colitis.
  • Helps stabilize blood sugars, at least in diabetic mice.
  • Helps you lose weight. Butyrate increases sensitivity the liver's to insulin, so the pancreas releases less insulin, the belly stores less fat, and fat pads all over the body release fatty acids more quickly.
  • Repairs "leaky gut." The linings of the small intestines can become “leaky,” allowing allergens and toxins to pass into the bloodstream. Butyrate feeds the barrier cells known as colonocytes and helps keep the lining of the gut strong.
  • Lowers LDL ("bad") cholesterol.
  • Lowers triglycerides.
  • Prevents colon cancer. Butyrate helps ensure that colon cells differentiate, which is to say, mature, into normal forms. The chemical also helps prevent mutations. The cancer-protective effect of butyrate is enhanced by docosahexaenoic acid (DHA), an omega-3 essentially fatty acid found in microalgae and fish oil. DHA should only be consumed in small amounts, no more than 1 gram per day, about the equivalent of 3 capsules of fish oil or 5 capsules of microalgae oil daily.
  • Reduces inflammation in other parts of the body. Certain healthy bacteria, especially Lactobacillus, have a calming effect on the central nervous system by sending it butyrates. The butyrates relieve stress, and stress reduction results in lower inflammation.
  • Relieves constipation. Fiber doesn't actually relieve constipation. The butyrates probiotic bacteria release from fiber relieve constipation. (This means that fiber doesn't help you stay regular unless your gut bacteria are healty.) The fiber from rye—which is usually OK in small amounts even on paleo diets—is especially useful for feeding the bacteria that make the butyrate that makes stools easier to pass and increases the frequency of bowel movement.
All that from mashed potatoes or boiled sweet potatoes or boiled winter squash. And maybe an occasional slice of 100% rye bread.

Starch isn't just about feeding you. It's also about feeding the probiotic bacteria that feed you nutrients you can't easily get in food. To get the benefits of starch, you need to establish probiotic bacteria in your gut by avoiding antibiotics to the greatest extent possible, and by eating fermented foods like sauerkraut and kimchi.

Maybe on some level our paleolithic ancestors knew that they needed to feed their healthy bacteria, too, and naturally sought out tubers. It didn't make them fat. 

Small amounts of the right carbohydrates prepared by boiling won't make you fat, either.

  • Gao Z and collaborators. Butyrate improves insulin sensitivity and increases energy expenditure in mice. Diabetes. 58(7). July 2009. 1509-17.
  • Suzuki T and collaborators. Physiological concentrations of short-chain fatty acids immediately suppress colonic epithelial permeability. British Journal of Nutrition. 100(2). August 2008. 297-305.
  • Photo courtesy of David Prasad by Flickr :
  • Photo courtesy of Patrick Collins by Flickr :

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