Our food industry works to bring you more and more ultra-processed foods that have little or no fiber, but there is no debate in the scientific community: you should eat lots of plants that have not had their fiber removed. A review commissioned by the World Health Organization (WHO) of 185 prospective studies and 58 clinical trials, covering 4600 adults, shows that for every 8-gram/day increase in dietary fiber, there was up to a 31 percent decrease in deaths from all causes, a 30 percent decrease in deaths from heart attacks, 22 percent reduced risk of stroke, and a 16 percent reduced risk of diabetes, colorectal cancer and breast cancer (Lancet, Jan 10, 2019).
The authors found no harm from a very high intake of high-fiber foods and feel that more fiber is better. Fiber is the structural material of plants that is found in all vegetables, fruits, whole grains, beans, nuts and other seeds. High-fiber diets are associated with:
• less overweight and obesity,
• lower systolic blood pressure, and
• lower cholesterol.
High-Fiber, High-Carbohydrate Foods are Healthful
The researchers showed that, compared to eating whole fruits, vegetables, grains and beans, eating sugar-added foods and refined carbohydrates in processed foods caused much higher rises in:
• fasting LDL and total non-HDL cholesterol concentrations that predict susceptibility for heart attacks,
• fractional cholesterol efflux that indicates increased plaque buildup in arteries,
• adipose tissue gene expression that shows increased deposition of fat in the body, and
• cytokine secretions, which are markers of inflammation (Lancet, Jan 10, 2019; Journal of Clin Endo & Metabolism, Sept 2018;103(9):3430-3438).
Other recent papers show that those who eat the most vegetables, fruits, beans and whole grains, which are full of carbohydrates, have the lowest rates of heart attacks and heart disease (Nutrition Journal, July 10, 2018;17:67). Eating whole fruits has been associated with the prevention and control of diabetes, even though many fruits are high in sugar (PLoS Medicine, April 11, 2017).
What are Carbohydrates?
Carbohydrates are single sugars or combinations of sugars. Glucose is an example of a single sugar. Sucrose or common table sugar is a double sugar. Starch contains thousands of sugar molecules bound together, while fiber contains millions of sugars bound together so tightly that you cannot break it down in your intestines.
Only single sugars can pass from your intestines into your bloodstream. Double, triple, other combinations of sugars and starches must first be split into single sugars before they can be absorbed. These reactions occur so rapidly in your intestines that most starches cause rises in blood sugar that are not much lower than those from single sugars.
Humans cannot absorb fiber in their upper intestines because they lack the enzymes necessary to break down fiber into single sugars. Therefore fiber passes unabsorbed in the intestines to the colon where bacteria do have the enzymes to break down some of the fiber. There are two types of fiber. Insoluble fiber cannot be absorbed and passes from your body, helping to prevent constipation. Colon bacteria are able to break down soluble fiber into short chain fatty acids (SCFAs) that reduce inflammation, helping to prevent diseases and prolong lives. A healthful diet includes large amounts of foods that contain both types of fiber.
Low-Carbohydrate and Ketogenic Diets Can Harm
Low-carbohydrate diets appear to increase risk for all-cause deaths by 15 percent, heart attacks by 13 percent and cancer by eight percent (European Society of Cardiology Congress, August 28, 2018, Munich Germany). The Atkins, Paleo and similar low-carb diets are unhealthful because they are low in fiber. A study from Boston that followed 15,428 U.S. adults aged 45-64 years for an average of 25 years found that low-carbohydrate diets shortened lifespans by four years (The Lancet Public Health, Aug 21, 2018;3(9):PE419-E428).
Those who got about 50 percent of their calories from carbohydrates lived the longest. Those who got more than 70 percent of their calories from carbohydrates were at increased risk for dying, presumably because the very-high-carbohydrate diets had more added sugars and refined carbohydrates. The authors also found that the death rate in the very-low-carbohydrate group increased as animal protein increased, and decreased as plant protein increased. People were more likely to die prematurely when they ate less carbohydrates and more animal protein, and their lives were extended when they ate more plants (vegetables, nuts, peanut butter and whole grains). Many older studies show that severely restricting all carbohydrates is associated with increased risk for premature death (Eur J Clin Nutr, 2012, 66: 694-700; Ann Intern Med, 2010, 153: 289-298; J Intern Med, 2007, 261: 366-374; Eur J Clin Nutr, 2007, 61: 575-581; PLoS One, 2013, 8:e55030).
Keto Diets Don't Help Athletes
How fast and hard an athlete can exercise depends on muscles using sugar for energy. A low carbohydrate diet depletes sugar stored in muscles and liver and so will tire and weaken athletes to impair performance both in training and in competition (J of Sports Medicine and Physical Fitness, April 4, 2018). See Keto Diet Not Likely to Help Athletes
• Base your meals on vegetables, beans, nuts, whole grains and whole fruits. Eat large servings of these fiber-rich foods, even if you are trying to lose weight.
• If you are still not getting enough fiber, don't try to correct the situation by adding fiber supplements, bran cereals or foods made with added ground-up fiber. Introduce more high-fiber whole foods into your diet gradually to avoid digestive discomfort.
• If you are trying to lose weight, are diabetic or have a problem with constipation, use whole (un-ground) grains instead of products made from flour, even if the label claims that they are "whole grain."