Several recent papers show that diets that restrict all carbohydrate-containing foods can cause diseases and shorten your life. People 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), partly because these foods are rich sources of soluble fiber (Nutr Rev. Apr, 2009;67(4):188-205).
1) Polish researchers followed 24,825 people, average age 47.6 years, for 6.4 years and found that those who ate the least carbohydrates, compared to those who ate the most, were 32 percent more likely to die prematurely from any cause, 51 percent more likely to die from heart attacks, 50 percent more likely to die from strokes, and 35 percent more likely to die of cancer. The same researchers then analyzed prospective studies of 450,000 people followed for an average 15.6 years and found that those who ate the least carbohydrates were 15 percent more likely to die from all causes, 13 percent more likely to die of a heart attack, and eight percent more likely to die from cancer (European Society of Cardiology Congress, August 28, 2018, Munich Germany).
2) 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 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 eaters were eating 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).
3) Compared to eating unrefined carbohydrates in fruits and vegetables, researchers showed that eating simple sugars and refined carbohydrates 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, markers of inflammation (Journal of Clin Endo & Metabolism, Sept 2018;103(9):3430–3438).
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).
Sugar in Fruits and Vegetables Is Safer than Sugar Added to Foods
Eating fruits and vegetables is associated with the prevention and control of diabetes (PLoS Medicine, April 11, 2017), even though they contain sugar. The most likely explanation is that sugar added to foods and in all sugared drinks (including fruit juices) causes an immediate overload of fructose that allows some fructose to pass unchanged from the intestines into the bloodstream and then directly into the liver, where fructose is converted to fatty triglycerides, which fill up the liver cells with fat. Fat in the liver prevents the liver from lowering high blood sugar levels the way it is supposed to do. The sugars in fruits and vegetables cause a slower rise in blood sugar because they also contain soluble fiber and antioxidants (Cell, January 9, 2014). The added sugars used in beverages and foods are the same as the sugars in fruits and vegetables, but when the sugars are extracted from their plant sources (sugar beets, sugar cane, maple trees, corn, flowers, grapes, apples and so forth), the beneficial soluble fiber and numerous antioxidants are removed.
Do Not Try to Restrict All Carbohydrates
It is harmful to your health to avoid complex carbohydrates that are rich sources of fiber. All carbohydrates are made up of sugars: singles, and chains of sugars ranging from two sugars bound together to thousands and millions of long chains of sugars. Unless you have a specific disease that requires a special diet, you should not restrict unprocessed plant foods that are full of fiber. Here are some of the diets that I do not recommend because they may harm you:
• Zero-Carb Diet means that you eat only meat and fat. Meat contains mostly saturated fats and avoiding fruits and vegetables deprives you of healthful soluble fiber. This is the most unhealthful diet yet.
• Ketogenic (Keto) Diet generally limits you to fewer than 50 grams of carbohydrates per day, which causes you to get most of your calories from fat and too few calories from fruits and vegetables, so you probably do not get enough soluble fiber. See Keto Diet Not Likely to Help Athletes and Keto Diets May Lead to Diabetes
• The Atkins Diet, where at first you are supposed to restrict carbohydrates so severely that you go into ketosis, later allows you to add back carbohydrates in some vegetables and fruits. My patients who have been on this diet have had a terrible time balancing how much carbohydrates to add back into their diets and they usually gain back weight that they have lost.
• Paleo Diets have many variations, but if you avoid grains, beans, seeds, fruits and many vegetables, as they usually advise, you will be deprived of soluble fiber. See Caveman Diet, Paleo Diet, Neanderthin
• A Low-Carb Mediterranean Diet may be the least harmful of the low-carbohydrate diets because you eat fats from plants that are mostly healthful mono-unsaturated and poly-unsaturated fats, rather than the saturated animal fats that many experts still feel are harmful to your health. You are encouraged to eat fatty fish, nuts, seeds and avocados.
• The Dukan Diet has so many rule changes that people often become confused and drop out. First you eat mostly high-protein foods, then you can add vegetables, then add fruit, then add whole-grain bread, then you are allowed to eat two unrestricted meals a week, and then you are allowed to eat foods from all food groups stressing oat bran.
• Various other low-carbohydrate, high-fat diets allow you to eat carbohydrates, but not very much. Although you are getting some carbohydrates, you may not be getting much soluble fiber and you may be eating too much animal protein and fat.
Healthful Soluble and Insoluble Fiber
Fiber is the structural material of plants that is found in all fruits, vegetables, whole grains, beans, nuts and other seeds. Before food can be absorbed from your intestines into your bloodstream, it must be broken down into basic building blocks. Since you lack the intestinal enzymes to break down fiber into its building blocks of basic sugars, you do not absorb fiber in your upper intestines. Fiber passes through your intestines into your colon where soluble and insoluble fiber are treated differently by the bacteria in your colon.
Soluble fiber dissolves in water and is readily fermented by enzymes produced by bacteria in your colon, so its breakdown products can be absorbed in your colon. Soluble fiber does all sorts of good things for you:
• It helps to control your weight by drawing water into your stomach to delay emptying and keep your stomach full, so it can decrease the amount of food that you eat.
• It helps to lower blood sugar and insulin levels. Since it draws water into your stomach to keep food there longer, it slows the rate at which your body absorbs sugar from your intestines. This helps to control blood sugar levels in diabetics and non-diabetics.
• It binds to sugars and starches in fruits, vegetables and seeds, which prevents much of the sugar from being absorbed in the intestines so it passes to the colon. There bacteria break down the soluble fiber, releasing the sugars so they can be absorbed. This delayed absorption markedly reduces the rise in blood sugar after you eat fruits, vegetables and grains, which helps to prevent diabetes or to control blood sugar in people who are diabetic.
• It is readily fermented in the right side of the colon to form short-chain fatty acids that help to reduce risk of colon cancer, inflammation and high cholesterol.
• It helps to prevent heart attacks by being fermented by bacteria in your colon to form short chain fatty acids that are absorbed into your bloodstream and travel to your liver to help prevent the liver from making the bad LDL cholesterol. Soluble fiber is the major food component we know of that lowers blood cholesterol when you add more to your diet.
• It adds water to the stool to help prevent constipation.
Insoluble fiber can absorb water but does not dissolve in it, so it is generally not fermented by bacteria or absorbed in your colon. Insoluble fiber adds bulk to your stool so can pass out from your body to help prevent constipation.
How Much Do You Need?
I do not recommend trying to count grams of fiber in your diet each day, but ideally you will eat at least 30 grams a day. Good sources of soluble fiber include dried peas, soybeans, beans, oats, rye, barley, figs, avocados, plums, prunes, berries, bananas, apples, pears, broccoli, carrots, sweet potatoes and onions. Good sources of insoluble fiber include wheat bran, beans, lentils, dried peas, nuts and other seeds, potato skins and most whole fruits and vegetables.
Don't worry about whether you are getting soluble or insoluble fiber; you need both kinds, and both are found in fruits, vegetables, whole grains and beans. If you're not getting enough fiber, don't try to correct the situation by adding fiber supplements, lots of bran cereal or foods made with added ground-up fiber. When you eat whole fruits, vegetables, whole grains and beans, you get all of the vitamins, minerals and phytochemicals nature packages with the fiber. Introduce more high-fiber whole foods into your diet gradually to avoid digestive discomfort.