In a new study from Japan, researchers found that both a low-carbohydrate/high animal protein diet and a high-carbohydrate/low animal protein diet were equally associated with increased death rates (Clinical Nutrition, September 23, 2020). This study followed 43,008 men and 50,646 women, ages 45-75 years, for 16.9 years. The diet that had the lowest total death rate and heart attack death rate was a plant-based diet that included plant sources of protein and fat as well as of carbohydrates. The authors noted that the carbohydrates in the participants’ meals were generally refined (e.g., white rice) since there is little market for whole grains in Japan. They also noted the Japanese preference for seafood over mammal meat. Even with those cultural differences, the basic findings of this study agree with many earlier studies showing that the most healthful diet is largely plant-based, limiting refined carbohydrates, processed foods and mammal meat (Amer J Clin Nutr, July 2011;94(1):49–57).
Healthful and Unhealthful Carbohydrates
Carbohydrates are single or double sugars or chains of up to millions of sugars tied together in a long chain. You can absorb only single sugars from your upper intestinal tract where you have intestinal enzymes that knock off single sugars one at a time from some carbohydrate chains such as starches, so they can be absorbed.
Healthful carbohydrates are found in all plants. They include fiber and other resistant starches that are made up of millions of sugar molecules bound together so tightly that they cannot be absorbed in your upper intestinal tract. These good carbohydrates pass to your colon where healthful bacteria have the enzymes to break them down and convert them into Short Chain Fatty Acids (SCFAs) that lower high blood pressure, high cholesterol, high insulin, and inflammation, to help prevent heart attacks and cancers and prolong your life. Soluble fiber also encourages the growth of healthful colon bacteria and discourages the growth of harmful bacteria (Cell Host Microbe , Dec 21, 2017).
Unhealthful carbohydrates are refined plant parts (usually whole grains or roots that have been ground into flour) and simple sugars that can be absorbed in your upper intestinal tract to cause high rises in blood sugar. When your blood sugar rises too high, sugar can stick to the outer membranes of cells throughout your body. Once stuck on a cell, sugar cannot get off the cell membrane and it eventually destroys that cell. This destruction causes all of the horrible consequences of diabetes and increases risk for heart attacks and certain cancers. In one study, a group of people over 65 who ate refined carbohydrates in a 60 percent carbohydrate diet for 4.5 weeks had a very significant rise in blood levels of the harmful LDL cholesterol that is associated with increased risk for heart attacks and premature death ( J of Clin Endo Metab , September 10, 2018;103(9):3430–3438). Refined carbohydrates such as sugared drinks or bakery products are fine as sources of energy for vigorous exercise, but most people in North America consume far more than they need, and as a result, seventy percent of our population is overweight.
Very Low-Carbohydrate Diets Can Harm
It certainly is healthful to restrict sugar and refined carbohydrates, but don’t go on a low-carbohydrate diet that encourages you to limit or avoid unrefined carbohydrates that are found in all vegetables, fruits, whole grains, beans, nuts and other seeds. You can be harmed both by eating lots of refined carbohydrates (sugar and flour) and by restricting unrefined carbohydrates from plants.
Switching from a normal balanced diet to a high-meat, very-low-plant carbohydrate diet reduced the amount of healthful colon bacteria such as Bacteroides, Clostridium, and Roseburia (Applied and Environmental Microbiology, September 21, 2018). These good bacteria break down soluble fiber to produce SCFAs and antioxidants that:
• prevent heart attacks by lowering cholesterol
• decrease inflammation
• block free radicals
• help to prevent DNA damage that can cause cancers such as colon cancer
• Eat lots of vegetables, fruits, unprocessed whole grains, beans, nuts and other seeds. These foods should not be limited even if you are trying to lose weight.
• Restrict refined carbohydrates such as bakery products (bread, bagels, pretzels, crackers, cookies, pastries), pasta, sugar-added foods and drinks, and other highly processed or refined foods.
• Unless you are a vegetarian, include seafood at least twice a week. Vegetarians should be sure to meet their needs for vitamin B12, which is not found in plants, by eating foods fortified with B12 or taking B12 pills.
• Avoid drinking anything with added sugar. (I also believe that you should avoid artificial sweeteners). The most healthful drink for quenching thirst is water.