What are good carbs and bad carbs?
First of all, food does not have morality, so they can’t be good or bad. However some carbohydrates provide a multitude of health benefits, and others just make your taste buds happy but do not do anything good for your body and some can cause disease if consumed in excess. To make sense of this first let’s start with a few definitions.
- Glucose: is one of three dietary monosaccharides (single sugar molecule) that make up all of our dietary carbohydrates. It is also the sugar found in our blood and the preferred fuel source for most of our cells.
- Sugars: these are carbohydrates made up of 1-2 saccharide molecules. They include glucose, fructose, galactose, maltose, sucrose, and lactose. They are also sometimes called simple carbohydrates. They are naturally occurring in fruits, some vegetables, other plants and dairy.
- Starches: large carbohydrate molecules made from multiple glucose molecules bound in chains. They take longer to be digested and absorbed than sugars and contain a lot of energy. They are found in grains and vegetables. Their digestion starts in the mouth and they are absorbed in the small intestine.⠀⠀⠀
- Resistant starches: these are starches that resist digestion and absorption in the small intestine due to their large size, complex shape and presence of fiber. They are then fermented by gut flora in the large intestine and produce short chain fatty acids that are the preferred fuel for large intestine cells.
- Fiber: this is the complex carbohydrate that is not digested. There are two types: soluble and insoluble. They are found in fruits, vegetables and grains. Some carbohydrates are inflammatory while others are anti-inflammatory.
Sugars and refined starches (those whose fiber has been removed, like white flour) can be inflammatory by the following mechanisms:
- As they are easy to digest, they raise blood glucose levels quickly and high circulating glucose causes the formation of Advanced Glycation End products or AGEs by binding with proteins. AGEs are pro-oxidants that can oxidize LDL cholesterol causing atherosclerosis (plaques) and DNA causing cellular damage.
- AGEs bind with receptors called RAGEs which signals nuclear factor kappa B ( NF-kB) to the nucleus which then promotes the transcription of cytokines like TNF alpha and IL-6 and others to trigger inflammation. Inflammation in adipose tissue causes insulin resistance. Insulin resistance further causes hyperglycemia. The more adipose tissue the higher the number of inflammatory cytokines.
- Some foods are naturally high in AGEs. Fried potatoes, cow milk, BBQ, roasted nuts are some. So AGEs can come from endogenous (within your body) production due to high circulating glucose or from high AGE foods. Fiber is a class of carbohydrates that are not digested by humans but they play many important roles in digestion and blood sugar control, in the gut microbiome and in mitigating chronic inflammation. They can be classified by molecule size: oligosaccharides vs polysaccharides or by solubility: soluble vs insoluble. Pectins from fruits, cellulose from vegetables, resistant starches from grains are other examples.
- Fibers pass through the small intestine undigested and enter the large intestine where gut bacteria ferment them into small chain fatty acids like butyrate. These small chain fatty acids are fuel for the large intestinal cells. It allows them to function properly and produce a sufficient mucous layer which protects them from pathogens. The fiber itself is fuel for favorable gut flora.
- Higher fruit fiber intake is associated with decreased intestinal mast cell activation indirectly through SCFA signaling and also directly by binding to mast cell surface and nuclear receptors. Mast cells are an important part of our immune system but chronic mast cell mediated inflammation is one of the main mechanisms in allergic and atopic conditions like asthma and eczema. High fruit intake is associated with improvement in asthma symptoms.
- Numerous epidemiological studies have shown an inverse relationship between fiber intake and serum levels of TNF alpha, CRP and IL-6 (remember those are inflammatory cytokines). Animal models have demonstrated wheat bran to be associated with elevated serum levels of the anti-inflammatory cytokine IL-10. This is an important emerging area of research but there is enough evidence to support including fiber rich carbohydrate foods like fruits and whole grains and a low carbohydrate diet may be deficient in some specific beneficial fibers. Oat beta-glucans are one such fiber. They are known to decrease cholesterol and fatty acid absorption in the large intestine thus increasing serum cholesterol usage and reducing circulating levels. Studies have shown that oat beta-glucans increase the activity of 2 potent antioxidant systems: glutathione peroxidase and superoxide dismutase, which inhibit lipopolysaccharide induced inflammation in intestines.
There may be a role for oat beta glucans in treating inflammatory bowel diseases. Oat beta-glucans also reduce PGE2 production (inflammatory prostaglandin) and reduced production of the pro-inflammatory cytokines IL-6 and IL-23. If you remember from my previous posts about cytokines and chronic disease IL-6 is associated with type 2 diabetes and obesity. IL-23 is implicated in many autoimmune diseases. Alpha-glucans and beta-glucans derived from some mushrooms are known to improve immune function by activating macrophages and Natural Killer cells. A supplement called AHCC which contains these alpha- and beta-glucans is under investigation for its ability to help the body eliminate HPV, the virus that causes cervical cancer.
I hope this article gives you some basis to make good decisions for yourself about what kind of food works for you and I hope you recognize that all carbohydrates are not equal.