Does Yogurt Reduce Cholesterol Levels?
~ March 1999 No.69 ~
Yogurt has gained a lot of popularity as another dairy product that is a good source of calcium and of course, protein. Yogurt can be found in the diary case with a wide variety of fat levels to satisfy those who are looking to reduce their calorie intake. You can even find yogurt that is made from soy milk if you are interested in getting more soy products into your diet.
Yogurt is perhaps one of the best known probiotic products. It is a probiotic because it contains live bacteria when eaten. Yogurt is made by adding at least two and sometimes three or four strains of bacteria to milk. These bacteria ferment the milk, lower its pH (make it more acidic), change its texture, and increase the digestibility of the milk proteins.
The observation that the Masii people of Africa have low serum cholesterol levels in spite of their diet that is rich in red meat and milk, prompted researchers to question whether milk and more recently fermented milk - like yogurt - could reduce serum cholesterol levels. This is not a straight forward question to answer because yogurt also contains fat, and fat in the diet is known to increase cholesterol levels.
Several scientific studies have been carried out to test whether yogurt consumption reduces cholesterol levels or not, but so far the results are not consistent. Part of the inconclusive results may be due to the different types of yogurt eaten. On the market today it is possible to buy yogurt that contains two bacteria - Streptococcus thermophilus and Lactobacillus bulgaricus, but some yogurts contain Lactobacillus casei and even bifido bacteria. Each bacteria is living and growing in the yogurt, but they must pass through the stomach in large enough numbers to be effective in the intestines. This is why to be an effective probiotic product it is generally agreed that there should be at least 10x7 bacteria/gram of product. That way, even if 90% of the bacteria die in the stomach, enough get through to have some effect.
There are at least two ways in which bacteria could affect serum cholesterol. As the bacteria in the lower intestines ferment, they produce compounds called short chain fatty acids or SCFA's. One SCFA - propionic acid in particular has been shown to decrease cholesterol synthesis in the liver. This would reduce the amount of cholesterol circulating in the blood. Some bacteria also have the ability to break down bile acids. Bile acids are secreted into the intestines but is re- absorbed and so most of the cholesterol is re-cycled back into the body. If the bile acids are broken down, the cholesterol is not reabsorbed but is flushed out in the feces.
It is not clear whether the bacteria found in yogurt can produce propionic acid in large enough quantities to affect cholesterol metabolism or whether they are capable of breaking down bile acids. More research needs to be done before the cholesterol lowering ability of yogurt can be proved or disproved.