Bill Harris, M.D. | Q&A
You've come smack up against one of the few real problems on a vegan diet: more fiber than your GI tract can handle. Fiber is mostly indigestible cellulose which is a long chain polymer of glucose. The fiber goes right through your small intestine and then dumps into the colon where there are bacteria that elaborate the enzyme cellulase. Cellulase splits glucose molecules off the ends of cellulose and the bacteria then metabolize the glucose, releasing gas and bowel irritants that lead to increased peristalsis, cramps, and diarrhea.
I don't know if your doctors have worked you up for celiac syndrome but even if they have I would recommend a trial of a gluten-free diet for a week or two. Gluten is a protein in most grains, particularly wheat, that generates an auto-immune reaction in about 5% of the population. If it goes on long enough there's microscopic damage to the intestinal lining, weight loss, and most of the symptoms you describe. I believe the vegan diet unmasks celiac syndrome in more people than the medical profession realizes and since there's nothing in grain that you can't get along without, it seems sensible to cut out all grains except perhaps boiled white rice for a couple of weeks and see what happens. If you're a celiac most of your symptoms may be gone shortly.
Beans are tasty and fairly nutritious but they contain two indigestible five carbon sugars, raffinose and stachyose that can also cause big time gas. In spite of their reputation as the protein source for veg*ns beans actually contain less protein per Calorie than leafy greens, the foods that should make up a large part of any healthy diet.
If you're eating the customary three squares a day it's possible that the meals are so large that they are simply overwhelming your digestive resources. A properly designed vegan diet based on vegetables and fruit rather than starches and grains and meeting Calorie needs is about 1/3 larger by weight and volume than an equicaloric omnivorous meal. Frequent small meals rather than three large ones work well for many people and more closely mimic the feeding patterns of our primate ancestors who were herbivorous arboreal grazers rather than carnivorous gorgers.
For someone with your symptoms it's very important to chew your food thoroughly so that it will be broken up mechanically and mixed with salivary amylase prior to swallowing. If you can't do that, a Vita Mix blender can turn out a very smooth, nutritious, and tasty mix of vegetables, seeds, and herbs meeting the RDA for all nutrients save B12. That problem can be fixed by adding a teaspoon of Red Star nutritional yeast. There's also an acidophilus product Töpfer Lactopriv/B Lactobacillus bifidus powder (vegan acidophilus substitute) available at health food stores. I haven't been much impressed with adding it to the blender as a digestive aid but it's worth a try.
I hope this will be of some help. If not, write again. I had similar symptoms for my first 25 years as a vegan which ended abruptly when I stopped eating bread and other glutinous grain products. That was after a gastroenterologist did a complete workup with tubes and gadgets in all available orifices and came up with the same diagnosis as yours, IBS.
-William Harris, M.D.
William Harris MD received a degree in physics from the University of California Berkeley, where he earned Phi Beta Kappa honors. He received his degree in medicine from the University of California at San Francisco, and received his postgraduate training at San Diego County Hospital. He holds a Medical License in the State of Hawaii. He has been an Emergency Department physican since 1963, and the Director of the Kaiser Permanente Vegan Lifestyle Clinic on Oahu until his retirement in 1998. Dr. Harris is the author of The Scientific Basis of Vegetarianism.
In addition, he was the 1950 Big Ten Trampoline Champion, is an accomplished hangglider and commercial pilot, and at age 70 became a skydiver with 108 jumps to date. Dr. Harris has been vegetarian since 1950, and vegan since 1963.