Munching on an apple is certainly a better alternative to chowing down on a brownie, but apples may have more fat-burning potential than meets the eye. This popular crunchy fruit that comes in so many varieties contains an ingredient that’s catching the eye of obesity researchers.
The compound, ursolic acid, abundant in apples, is found in a few other fruits such as prunes and cranberries as well as the spices basil and oregano. Apples are one of the best sources – but you won’t get it if you peel the apple. Ursolic acid is mainly found in the outer skin or peel of the apple.
What’s so special about ursolic acid? In a recent study, researchers fed three groups of mice a high-fat diet, letting them eat as much as they want every day for 6 weeks. The only difference was two groups of mice supplemented their diet with either a moderate or high dose of ursolic acid. The lowest dose being about 6% of the amount of ursolic acid in a medium-size apple.
Here’s where it gets interesting. Even though mice supplemented with ursolic acid ate more food, they gained less weight and had greater strength and exercise capacity. Regardless of dose, the ursolic-supplemented mice maintained a better body composition.
Researchers noted the mice supplemented with ursolic acid had a higher resting metabolic rate, which they attributed to activation of brown fat. Unlike white fat, the jiggly kind of fat we want to see less of, brown fat is a metabolically inefficient form of fat. When burned, the fat that would normally be converted to energy is released as heat. This inefficient form of fat, when turned on, sets the stage for burning more white fat, the kind we want to get rid of.
How much brown fat do most people have? Babies have the most brown fat while adults have less of this desirable form of fatty tissue that doesn’t add inches to your waistline. Most of us have small areas of brown fat around our collarbones. Brown fat is most active during infancy as a way to generate heat to keep a baby warm, but it becomes quiescent with age, at least in most people. Research shows leaner people have greater brown fat stores and activate it easier than obese people even during adulthood. In animal studies, activation of brown fat offsets some of the negative metabolic complications of obesity. As a result, brown fat has lots of untapped potential – when it can be turned on.
Interestingly, mice supplemented with ursolic acid not only gained less fat, but they also became stronger. According to studies, ursolic acid also has an added benefit – it has an anabolic effect on muscle tissue. In fact, researchers are looking at it as a way to reverse muscle atrophy, loss of muscle tissue due to illness or aging. It seems to boost muscle growth by stimulating the release of insulin-like growth factor 1, or IGF-1, a protein produced by the liver that ramps up muscle protein synthesis.
If there’s one thing that catches the attention of bodybuilders and fitness buffs, it’s something that increases fat loss and boosts strength or muscle size – a desirable combination! Unfortunately, studies looking at ursolic acid’s effect on body composition in humans are limited. One study published in a Korean journal looked at the effects of ursolic acid in supplement form.
In this study, participants were 16 healthy males who had strength trained for several years prior to the study. Both groups followed a rather intense weight training routine – 5 sets of 26 exercises at around 70% of one-rep max performed each day of the week with one day off for 8 weeks. One group took a ursolic acid supplement at each meal while the other group took a placebo.
The results? At the end of 8 weeks, the ursolic acid group lost more body fat than the placebo group and had a small increase in lean body mass but significant increases in strength. The ursolic acid group also had higher levels of IGF-1 and another protein called irisin, released by muscle cells during exercise. Irisin may explain some of the health benefits of exercise. For example, irisin seems to activate brown fat as well as improve memory and cognition by triggering the growth of new neurons in the brain and central nervous system. So closely is irisin linked with exercise that it’s sometimes referred to as the “exercise hormone.”
One way ursolic acid may offer its potential benefits is by increasing IGF-1, an important mediator of muscle protein synthesis and by stimulating a greater release of irisin, a protein that makes brown fat more active – a definite advantage if you’re trying to lose body fat. Some evidence suggests irisin itself can turn on hormones that convert white fat to brown fat.
Another “trick” to turning on brown fat is exposing your body to cold temperature. In humans, spending time in a room 60 degrees Fahrenheit “wakes up” quiescent brown fat so it can start producing heat. Of course, not everyone is comfortable hanging out in a room that’s 60 degrees F. or less for hours. That’s why compounds like ursolic acid naturally found in apple peels are so intriguing. Don’t forget that exercise itself, especially aerobic exercise, releases irisin too, which turns on brown fat. Exercise in the combination of ursolic acid may ultimately prove to have benefits for fat loss and strength gains in humans, although more human research is needed.
Until more is known, get ursolic acid naturally by eating apples. Apples are loaded with fiber to help fill your tummy up. In fact, a study found eating an apple prior to a meal reduced calorie intake by 91 calories – but be sure to leave the skin on – that’s the part that has the ursolic acid – and when you finish your apple lace up your exercise shoes because working up a sweat also activates brown fat and helps you get leaner.
References:
Fitness RX. August 2015. “Chemical in Apples Promotes Fat Loss”
The Wall Street Journal. “Fat Fighting Is Part of the Apple’s Peel”
Nutritional Journal. “Ursolic acid is anabolic; increased strength, reduced body fat”
Korean J Physiol Pharmacol. 2014 Oct;18(5):441-6. doi: 10.4196/kjpp.2014.18.5.441. Epub 2014 Oct 17.
Psychology Today. “Irisin: The “Exercise Hormone” has Powerful Health Benefits”
Scientific American. “Supercharging Brown Fat to Battle Obesity”
Diabetes July 2009 vol. 58 no. 7 1482-1484.
Cell Metab. 2014 Feb 4;19(2):302-9. doi: 10.1016/j.cmet.2013.12.017.
Appetite. 2009 Apr; 52(2): 416-422. Published online 2008 Dec 6. doi: 10.1016/j.appet.2008.12.001
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