Thursday, June 30, 2011
Image: Example of an Ishihara color test plate. The numeral "74" should be clearly visible to viewers with normal color vision. Viewers with dichromat or anomalous trichromat may read it as "21", and viewers with achromat may see nothing.
Unusual bleeding or discharge is one of the classic seven warning signs of cancer. Blood in the stool could be a sign of colon cancer. It's also a common sign of diverticulosis of the colon. Unfortunately, people with red-green color blindness might not notice that they are passing blood with their bowel movements. Here's an article about three color-blind men who didn't notice that they were passing blood with their stool. One of them had colon cancer. Another had diverticulosis; he was bleeding heavily but mistook the blood for diarrhea. The third patient had bleeding from hemorrhoids. The men didn't notice the blood because they can't see the color red. Fortunately, their wives saw the blood and had them seek medical attention.
Red-green color-blindness is far more common in men than in women. That's because men have only one copy of the X chromosome in each of their cells. If one of the genes on their X chromosome is defective, they don't have a spare X chromosome to serve as a backup. Women don't get red-green color-blindness unless they inherit a defective version of the gene from both parents. That's why women rarely get red-green color-blindness, but even a woman with normal color vision can have color-blind sons.
There's no way to fix color-blindness. Fortunately, the intestinal problems that these men had are preventable by diet. Colon cancer is rare in populations that eat a low-fat, plant-based diet. So are diverticulosis and hemorrhoids, which result from constipation.
Sunday, June 12, 2011
A recent article in the New York Times argued that gorillas stay slim because they eat a high-protein diet. While I'm glad to see someone else point out that a plant-based diet provides adequate amounts of protein, I'm annoyed to see scientists and journalists misunderstand and misrepresent the real significance of this fact. It's as if they haven't read the basic literature on nutrition and can't understand arithmetic.
Yes, the gorilla's natural diet is high in protein, as a percentage of calories. However, the gorillas' natural food tends to be low in calories, because the calories are diluted by water and fiber. Gorillas have to eat an enormous amount of food every day to get enough calories. When human volunteers tried to eat a gorilla-style diet for a short period of time to see how it would affect their cholesterol levels, they had to spend more than 8 hours a day eating, just to get enough calories to keep from losing weight during the trial. Gorillas stay slim because of the high fiber content and low fat content of their food, not because of the balance of protein to carbohydrate in their food!
The biggest dietary challenge for a gorilla, as for any leaf-eater, is to get enough calories. When they eat a relatively high-protein diet, they just end up converting the excess protein to sugar and burning it for energy. Unfortunately, protein is "dirty sugar." Burning protein for energy produces waste products such as urea and sulfuric acid.
People can stay very slim on a high-carbohydrate diet, if it is also high in fiber and low in fat. For example, when Chris Voigt of the Washington State Potato Commission decided to go on a potato-only diet as a publicity stunt, he figured that he had to eat 20 potatoes a day. In practice, he found it really hard to eat his entire potato ration, because potatoes are so filling. As a result, he lost a lot of weight. Even when he made an effort to eat his entire potato ration every day, he continued to lose weight. That's because a starchy diet improves insulin sensitivity and thus revs up your metabolism. People who eat starchy diets burn more calories than people on fatty diets. Voigt lost 21 pounds during his 60-day potato diet. His cholesterol levels, triglyceride levels, and even his blood sugar levels decreased!
According to the New York Times, Dr. Raubenheimer claimed that modern societies “are diluting the concentration of protein in the modern diet. But we eat to get the same amount of proteins we needed before, and in so doing, we’re overeating.” What nonsense!
Nutrition scientists have known for more than 100 years that human protein needs are modest and are easily met by any reasonable plant-based diet. Also, the societies with the biggest problem with obesity are also the ones with the highest protein intake! Modern societies are consuming too much fat and too little fiber. Animal foods are a big offender, because they contain fat but no fiber and usually no digestible carbohydrate. Refined foods are also a big offender, because they represent the concentrated calories from plants--with the fiber and other wholesome things stripped out.
The take-home lesson from the gorilla story shouldn't have been that people need to eat more protein. It's that people need to eat plants. If people don't want to spend 8 hours a day eating leafy vegetables, they can eat some nice, filling potatoes or other starchy staples along with plenty of vegetables and fruit.