"Just an avocado a day can significantly lower your cholesterol and reduce the risk of heart disease a new study shows. Avocados are rich in socalled healthy fats and other nutrients and the study published in the Journal of the American Heart Association shows the creamy fruit can work within weeks to lower cholesterol. Just like olive oil and nuts avocados have plaquebusting monounsaturated fatty acids and the effects seem similar to all the benefits from a Mediterranean diet the researchers said. And its one more piece of evidence in favor of adding good fats to the diet.  In the past we used to substitute carbohydrate for saturated fat and that would result in a lowfat diet said Penny KrisEtherton chair of the American Heart Associations Nutrition Committee and distinguished professor of nutrition at Pennsylvania State University. Now were seeing that its better for people to have good fats in their diet at the expense of saturated fat. And so the current message is to replace saturated fat with unsaturated fat and in so doing consume a moderatefat diet not too much and also not too little KrisEtherton told NBC News. KrisEtherton and colleagues did an intensive study with  typical Americans  all overweight or obese but with healthy cholesterol and blood pressure levels. Its tough to test diets in real life because people eat so many different things but the team controlled what everyone ate feeding them carefully calibrated diets. One was a lowerfat diet without avocado another was a moderatefat diet without avocado and the third added one avocado per day to the moderatefat diet. The two moderatefat diets looked a lot like the average American diet with about a third of calories coming from fat. The lower fat diet provided  percent of calories from fat. Everyone spent five weeks on each diet. No one lost weight but their lowdensity lipoprotein LDL or bad cholesterol levels changed.  All diets decreased LDL cholesterol the main lipid risk factor for cardiovascular disease. But the diet with the avocado decreased LDL cholesterol the most KrisEtherton said. Americans are advised to keep total cholesterol below  and preferably below  http_UCM__Article.jsp. LDL should be below .  While they were eating the avocadoaday diet the volunteers saw their LDL go down by more than  points compared to their usual levels KrisEthertons team reported in the Journal of the American Heart Association. LDL was . points lower on the moderatefat diet without the avocado and . points less on the lowerfat diet. The volunteers all ate Hass avocados which have bumpy green skin. The Hass Avocado Board helped pay for the research which was also funded by the U.S. government.  In addition to monounsaturated fats the avocados contain fiber phytosterols and polyphenols  all of which can help lower cholesterol. Avocados also contain natural sugars that may help regulate blood sugar. We need to focus on getting people to eat a hearthealthy diet that includes avocados and other nutrientrich food sources of better fats KrisEtherton said. All the foods were exactly the same except the avocado versus oils that were high in monounsaturated fat on the moderatefat diet. So that was the only difference between the two diets which then tells us that its the avocado that has additional benefits which are beyond the unsaturated fat. The findings are similar to a batch of studies http that showed people who were given olive oil and nuts and told to add them to their diets ended up healthier httpvitals.nbcnews.com_newstastydietcutsheartdiseasestudyfindslite. They were less likely to have strokes or heart attacks and they were less likely to die  http a period of years than people who didnt get the extra oils. Saturated fat  the kind found in meat and butter  has a different chemical structure from the unsaturated fats found in plant products. Repeated studies have shown it raises the risk of heart disease. We studied avocados but maybe a lot of other fruits and vegetables have these bioactive components which have additional cholesterollowering effects KrisEtherton said. And certainly theres an emerging research base showing that some of these bioactive components may affect another lipoprotein particle favorably like highdensity lipoprotein. I think we need to stay tuned for that.  Americans may not be used to eating avocado but KrisEtherton says its easy to add. Consumers can include avocados in their diet in salads. They can include avocados on top of a sandwich or in a sandwich. They can make guacamole and use vegetables rather than chips as the dip she said. I love guacamole and with my recipe Ill use avocados cilantro lime juice and garlic... and then sometimes Ill put salsa in or red pepper flakes. But like anything too much of a good thing can be harmful. Avocados are definitely not lowcalorie food. One avocado has around  to  calories. So I would strongly urge people not to just add an avocado a day to their diet but they have to substitute nutrientpoor calories which are so popular in the U.S. diet. KrisEtherton said. Erika Edwards contributed to this story"