Week of March 12, 2012
Contact: Alice Bender, (202) 328-7744

AICR HealthTalk
Karen Collins, MS, RD, CDN
American Institute for Cancer Research

Q: Is it true that grass-fed beef contains a healthier type of fat than the fat found in standard grain-fed beef?

A: Grass feeding does increase meat's content of omega-3 fat (the healthy fats found naturally in greatest amounts in fatty fish like salmon), though the actual amount of these fats is not large, so the importance of this difference is not yet clear. A small randomized controlled trial in Ireland did find increased blood levels of omega-3 fats in adults eating grass-fed beef and lamb for four weeks compared to those eating the same amount of beef and lamb from animals fed a grain-soy concentrate. The study also showed a decreased ratio of omega-6 to omega-3 fats in blood values; some research suggests this ratio might be a factor in inflammation. The study kept total red meat consumption to no more than 18 ounces per week to meet recommendations of the AICR for lower risk of colorectal cancer. Three servings per week of grass-fed meat resulted in total consumption of the healthy "long chain omega-3 fats" that averaged 65 milligrams (mg) compared to 44 mg per day reached by the conventional-fed beef group. The U.S. 2010 Dietary Guidelines recommend an omega-3 fat daily intake of at least 250 mg. Some analyses report grass-fed beef also contains three times as much CLA (conjugated linoleic acid) as grain-fed beef, but grass-fed beef in the recent Irish study was no higher in CLA, and blood levels of CLA did not increase in those who ate it. Preliminary lab studies suggest CLA might reduce growth of cancer cells, but effects in humans are not clear yet, nor are what amounts would have an impact. All beef comes from cattle that consume grass most of their lives; conventionally produced beef comes from cattle that spend the last four to six months of life in a feedlot eating a mixture of grains and soybeans. "Grass-fed" beef comes from cattle that spend their entire lives feeding on grass or forage. People choose grass-fed beef for a variety of reasons, but we really don't know yet how much health impact the difference in fat content provides.

Q: Will I burn more calories if I run instead of walk?

A: If you go the same distance, studies show you will burn the same calories regardless of whether you walk or run. Of course, it takes more time to cover the same distance walking than running, so in the same amount of time, you'd burn more calories running. The intensity of your activity also influences how many calories you burn: going uphill for the same distance and same amount of time uses more calories than on a completely flat area or treadmill setting. Another option for burning more calories is "interval training," which interjects a few short one- or two-minute bursts of more intense activity into moderate activity. (Those bursts could come from jogging, fast walking or climbing hills.) The American College of Sports Medicine and American Council on Exercise say that, as long as you start and end with five to ten minutes of warm up and cool down, interval training can be a good way to increase fitness without long periods of running. As with beginning any new exercise, start slowly and gradually work up to longer times and more intensity. If you are considering running be aware of the potential impact on knees and other joints. If you want to try interval training, be sure to discuss this with your doctor if you have medical problems that may put you at risk.

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