On Nutrition

DEAR DR. BLONZ: I just read a book that says by blending fruit into a smoothie, you are not getting the benefits of the fruit's insoluble fiber because the blender completely destroys it. The book also says that not only am I not getting the fruit's full fiber benefit, but also the sugar from the fruit enters my bloodstream just as quickly as fruit juice. Is this true? Should I quit making smoothies? I get two of my daily fruit servings from my smoothie. Is there a better solution? -- K.S.D., via email

DEAR K.S.D.: I don't buy the argument that blending negates the benefits of the fiber in fruits (or vegetables or grains). The machine will most certainly reduce the size of fiber particles, but the fiber is still there. It is the unique way that the fiber molecules are bound together that's the key. Digestive enzymes help break down large compounds into ones small enough to pass through the absorptive surfaces in the intestines. Fiber is unique in that the human body doesn't have any enzymes to break it apart. We do, however, have the enzymes to effectively break down starch into its individual glucose units.

As a result, fiber gets to pass through the small intestine without being absorbed. The blender does indeed cut and shred, but there is no basis to fear that this process breaks down the molecular bonds that form the essence of the fiber.

Blending does effectively increase the viscosity (thickness) of the food as compared with a typical juice or with the product of a juicer, where the fruit's solids are not a part of the final output. Higher viscosity tends to slow the rate at which we eat, as well as the rate at which the stomach empties. Both these factors lead to less food being consumed before you feel full.

Eating fruits, vegetables and whole grains are the heart of what healthful eating is all about. One question associated with smoothies, which you mention, is whether consuming foods in this manner might cause the blood sugar level to rise more rapidly than eating the same foods in the whole, unblended state. The research is somewhat mixed on this matter, and considering the benefit of having these healthful foods in your diet, it makes sense to consider a few more specifics.

What, for example, are the ingredients in your smoothies? You say that you have been consuming fruits this way for a while. Is having smoothies as a regular part of your diet working for you? Do you have any health issues relating to blood sugar regulation? If so, then you should modify the components of your drink.

The great thing about the smoothie concept is the wide variety of wonderful sweet or savory recipes available, including the use of fruits, greens, grains, protein sources and spices (see tinyurl.com/kaduhn7). There are also plentiful recipes for those who want their smoothies strictly vegan (see tinyurl.com/lm4dk7y). As with any food, make it one part of a healthful "big picture." As always, eat slowly and enjoy.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Should there be any concerns about eating baked potato peelings? I wash and prick holes in my potatoes, then put them in a sandwich bag with a little water and cook them in the microwave. The resulting peel is soft and I enjoy the taste, often seasoning it with garlic or onion, salt and pepper. -- S.T., Redding, Calif.

DEAR S.T.: The vitamins, minerals and fiber in a potato come primarily from the flesh. Although not a nutrition powerhouse, the peel does contain a small amount of iron and fiber, and it provides a good contrast to the smooth texture of the flesh. There's absolutely nothing unsafe about eating potato peels provided they are clean, free from sprouts and have no greenish discolorations.

The green aspect is particularly important as potatoes can produce solanine, a bitter-tasting toxin that affects the nervous system. Solanine is produced when the potato is exposed to sunlight or allowed to sprout. It is most concentrated in the sprout, but it's also present in potatoes having a greenish tint to the skin. The solanine itself isn't green, but when that color is present, it indicates that the sprouting process has begun. You can slow the production of solanine by storing your potatoes in a cool, dark place. Carefully cut away all sprouts and green portions before cooking. And discard any potatoes that taste bitter.

Regarding your plastic bag cooking technique, I trust you have already read the carton or checked with the manufacturer to verify that the product is safe for microwave use. All plastic bags are not the same, and a number of brands will melt in the microwave.

DEAR DR. BLONZ: Is it all right to combine fruits and vegetables together in blended drinks for breakfast, lunch or dinner? -- B.H., San Diego, Calif.

DEAR B.H.: Yes, but from a taste perspective, it helps to do some experimenting to see which combinations work best.

DEAR DR. BLONZ: How much fiber and fat is in an avocado? Also, what is the minimum amount of saturated fat that a person should have in his or her diet? -- R.M., Oakland, Calif.

DEAR R.M.: There are many avocado varieties on the market, each having different qualities of flavor and texture. There tend to be generic differences, however, between the varieties grown in California and Florida. Florida avocados tend to be larger in size, with less fat, protein and slightly more carbohydrates than a comparable serving of California avocado. A 100-gram (3.5-ounce) portion of a California avocado will contain 6.8 grams of fiber, and 167 calories from 2 grams of protein, 8.6 grams of carbohydrate and 2.1 grams of saturated fat, 9.8 grams of monounsaturated fat, and 1.8 grams of polyunsaturated fat.

That same 100-gram portion of a Florida avocado contains 5.6 grams of fiber and 120 calories from 2.2 grams of protein, 7.8 grams of carbohydrate and 2 grams of saturated fat, 5.5 grams of monounsaturated fat, and 1.7 grams of polyunsaturated fat.

As for your second question, the human body has no minimum requirement for saturated fat.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: My hairstylist recommended I get a biotin supplement to help strengthen my hair. I would like some insight as to whether this makes sense, and if so, why I hadn't heard of this until now. -- V.H., Oakland, Calif.

DEAR S.F.: Biotin is a vitamin that plays a role in the metabolism and synthesis of fats, amino acids and carbohydrates. As such, it is important that we have this nutrient in our diet. Biotin, however, is only needed in small amounts, and deficiencies are rare. An adequate intake of biotin for adults is 30 micrograms per day (one microgram is one millionth of a gram). Symptoms of a biotin deficiency include hair loss and skin rashes, but if there's no deficiency to start with, there is no evidence that taking amounts above normal body requirements can solve hair, skin or nail problems.

Foods that contain biotin include organ meat, oatmeal, egg yolks, milk, soybeans, peanuts, whole grains, fruits and vegetables. It is also known that biotin can be synthesized by the bacteria that live in our large intestine, though it's unclear how much of this biotin we actually absorb.

While we are on this topic, here is an interesting side note about biotin and eggs. While egg yolks are a good source of biotin, there is a compound in raw egg whites, called avidin, that prevents biotin from being absorbed. Biotin deficiencies have been found in individuals who consume large quantities of raw egg whites. Perhaps this was nature's way of keeping the fox out of the hen house.

DEAR DR. BLONZ: Can vitamin K creams help remove spider veins? -- C.S., Berkeley, Calif.

DEAR C.S.: Spider veins are small red blood vessels usually found on the legs near the skin surface. They fan out from a small branch of a blood vessel near the surface. Treatment involves locating and disrupting the blood supply. Spider veins are not a sign of poor health in and of themselves, but they can be a source of embarrassment.

Vitamin K plays a role in blood coagulation (clotting), and current treatments of spider veins involve coagulation, or blocking the blood flow to the visible vessels. One medical technique uses a laser to "photo-coagulate" the master vessel feeding the veins, while another uses a saline injection to bring about the desired blockage.

The idea that an externally applied vitamin K cream might clear up spider veins seems straightforward, but there is little in the way of evidence to support this use. It is also not advisable to take vitamin K by mouth in the hopes that it can eliminate spider veins. As a caution, individuals with a blood-clotting disorder, or those taking anticoagulants, should speak with their physician before using any product containing vitamin K.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.