Ask Tufts Experts: Prunes and Regularity; Caffeine Sensitivity

My mother used to drink prune juice to help with regularity. Now I’m hearing people talk about prunes again. Is there really something special about prunes?

Alice H. Lichtenstein, DSc, Stanley N. Gershoff professor of nutrition science and policy at Tufts’ Friedman School, answers: “Your mother was right! Randomized controlled trials have found that eating prunes or drinking prune juice helps with stool consistency and increases stool frequency. Prunes (dried plums) contain both soluble and insoluble fiber, as well as the natural sugar alcohol sorbitol. Sorbitol draws water into the colon and soluble fiber forms a gel with that water, making the stool softer and easier to pass. Insoluble fiber stimulates movement in the intestines.

“Consuming prunes may be more effective than drinking prune juice because some of the fiber is lost during the juice-making process.

“If you would like to try prunes or prune juice to ease constipation, try five to 10 prunes or one-half to one cup of prune juice a day. Some people experience increased gas and diarrhea after prune consumption, although participants in randomized controlled trials did not report these effects. Start with a low amount, see how it works, and increase if necessary and tolerated. One study noted improvement after only one week. If you don’t see improvement after several weeks, or your condition worsens, consult your health-care provider.”

In the June article on coffee, you mention avoiding coffee in the afternoon “if you are sensitive to caffeine.” How do I know if I’m sensitive to caffeine?

Judith C. Thalheimer, RD, LDN, executive editor or Tufts Health & Nutrition Letter, answers: “If you are sensitive to caffeine, you will know it! Caffeine is a stimulant that acts on the central nervous system, so too much can cause your heart to race, make you feel jumpy, nervous, or restless, and disrupt sleep. Most people can consume up to 400 milligrams of caffeine a day (which is about four eight-ounce cups of coffee or 15 cups of regular tea) without experiencing adverse effects, but people with caffeine hypersensitivity can experience these symptoms after consuming even small amounts of caffeine. Symptoms may last several hours.

“Ninety-nine percent of caffeine you consume is absorbed within 45 minutes. The amount of caffeine in your blood peaks between 15 and 120 minutes after you consume it. Caffeine is metabolized in the liver, where it is turned into other compounds that are removed from the body in urine. The ‘half-life’ of caffeine (the amount of time it takes for half of the caffeine you ingest to be broken down) ranges from one-and-a-half to nine-and-a-half hours. This wide range is due to a number of factors, but genetics likely accounts for the majority of differences in caffeine sensitivity. Variations in some specific genes (called CYP1A2 and ADORA2A) have been found in people with ‘fast’ or ‘slow’ caffeine metabolism and ‘high’ or ‘low’ caffeine sensitivity.

“People who don’t regularly consume caffeine are likely to be more sensitive than habitual consumers, and pregnancy and use of oral contraceptives can increase caffeine sensitivity. As we age, caffeine may be broken down by our bodies more slowly. This slower clearance could enhance the effect of the older adult’s habitual coffee intake.

“Coffee drinkers tend to like the increased wakefulness and sharpened thinking they get from caffeine (although they may not be aware that caffeine can reduce fine motor coordination and is known to decrease reaction time). If you suspect caffeine is affecting you in ways you don’t like, cut back, switch to decaf or half-caf, or wean yourself off coffee (and caffeinated teas and soft drinks) altogether. (Wean yourself slowly and watch out for withdrawal symptoms like headache and “brain fog,” fatigue or drowsiness, decreased energy and alertness, depressed mood, difficulty concentrating, and irritability.)”

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