The WHY Behind the Findings
Calcium and Weight Loss * Trans Fats and Heart Disease
Ever since I was a young girl and babysat toddlers, I’ve
always marveled at young children’s natural curiosity. Have you ever played the
why game with a toddler? No matter how many answers you give, there is
always the very predictable response: Why? I clearly remember playing
several why games with my nephews. Why do you have to leave?
Because I have to go to work and if I don’t leave right now I’ll be late. Why
do you have to work? Because I have bills to pay. Why do you have
bills? — You get the picture. For this month’s thought bullets, I did some
research to try to answer the why question behind some nutritional news
hitting the headlines frequently in recent months: a possible link between
increased calcium intake and weight loss and the reason trans fats are
associated with an increased risk of heart disease.
Calcium and weight loss
A Danish study found a possible mechanism that could explain why some studies find that an increased intake of dairy products results in reduced body weight. The researchers in Denmark found that calcium could reduce body weight by binding fat in the intestine and increasing fat excretion from the body.
The results of the study were published in the March 2005 issue of the International Journal of Obesity. The study found that fat excreted in the feces increased 2.5-fold in people on a high calcium diet compared to a low calcium diet. Low fat dairy products supplied the majority of the calcium in the study.
Arne Astrup, one of the lead authors of the study stated, “I had this hypothesis that calcium could bind fat in the GI tract and had to find out if it could affect weight through fecal fat excretion. But it surprised us that it was so much.” (interview with NutraIngredients)
Limitations of the study included a small sample size (10 subjects), and short duration (subjects spent one week each on three diets of varying calcium and protein composition).
Trans fats and heart disease
Trans fatty acids (trans fats) are formed when liquid vegetable oils go through a chemical process called hydrogenation. Hydrogenated vegetable fats offer advantages to food processors including being solid at room temperature which can improve the quality of some baked foods as well as increasing the food’s shelf life.
Mounting evidence suggests trans fats raise LDL cholesterol (the so called bad cholesterol). In 2003, Denmark became the first country in the world to restrict the use of hydrogenated fats. Oils and fats are not allowed in Denmark if trans fats exceed two percent. In the United States, trans fats in foods must be included on the nutritional label staring January 1, 2006.
Scientists recently discovered a molecular series of events in the liver that may explain how diets rich in saturated fats and trans fats can increase blood levels of cholesterol and triglycerides, which can lead to an increased risk of heart disease.
Reported in the January 2005 issue of Cell, the study identified a cascade of biochemical signals, starting with the activation of PGC-1beta (a specific co-activator protein). Scientists explain that PGC-1beta acts like a dimmer switch that varies the brightness and darkness of a light. Although very complex, the scientists believe that saturated and trans fats cause greater activity in the gene that makes PGC-1beta co-activator and starts the cascading events that direct the liver to manufacture more cholesterol, which it does in the form of lipoproteins, These lipoproteins lead to high blood levels of cholesterol and triglycerides.
Some scientists believe that PGC-1beta is a sensor for saturated fats and trans fats, other scientists hypothesize PGC-1beta is actually only interpreting signals from other sensors that are still not fully understood. One thing is certain: the coactivator protein PGC-1beta will receive further study.
Jacobsen R, Lorenzen J K, Toubro S, Krog-Mikkelsen I, Astrup A. Effect of short-term high dietary calcium intake on 24-h energy expenditure, fat oxidation and fecal fat excretion. International Journal of Obesity. 2005;29(3):292-301.
Calcium mechanism for weight loss gets clinical support, www.nutraingredients.com, newsrelease on February 25, 2005.
Lin J, Yang R, Tarr P T, Wu P-H, Handschin C, Li S, Yang, W, Pei L, Uldry M, Tontonoz P, Newgard C B, Spiegelman B M. Hyperlipidemic Effects of Dietary Saturated Fats Mediated through PGC-1$ Coactivatoin of SREBP. Cell. 2005;120:261-273.
Harmful mechanism behind trans fats unlocked. www.foodnavigator.com, newsrelease on February 3, 2005.
Fat pathway clarified. www.biomedcentral.com, newsrelease on January 31, 2005.
Compiled by Betty Holmes, MS, RD
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