An apple a day may keep the doctor away, but can it also help you build muscle? We know that apples contain an abundance of vitamins, minerals, and phytonutrients, but as a protein source, they don’t stand out. In fact, a medium apple only has a half-gram of protein. Based on protein content alone, apples won’t do much to boost muscle hypertrophy. Plant-based foods offer protein, but apples aren’t a substantial source. So, how could apples help with muscle hypertrophy?
Are Apples Anabolic?
About seven years, scientists were looking for natural, diet-related compounds that help reduce muscle atrophy. As you know, muscle loss of muscle size and strength is a big problem for older people and also those who are confined to bed for long periods of time. Being relegated to bed rest means you can’t exercise, so muscle atrophy quickly sets in. While looking for compounds to help prevent muscle loss, researchers came upon ursolic acid. To their surprise, they found ursolic acid turns on genes that activate muscle protein synthesis. Also, ursolic acid dials back expression of ATF4, a protein that causes muscle atrophy and loss.
To see if ursolic acid would work in live animals, they gave this compound to rats in their regular food for five weeks. By the end of the study, the mice that got the ursolic acid experienced greater increases in muscle size than those who didn’t. We know that muscles grow when a pathway called the mTOR pathway is turned on. Interestingly, research shows that ursolic acid extends the activation of the mTOR pathway in response to strength training. So, muscles work a little harder to lay down new muscle tissue in the presence of ursolic acid. Ursolic acid works in two ways. It turns off genes involved in muscle atrophy and the activity of the mTOR pathway.
The way ursolic acid activates the mTOR pathway is by increasing IGF-1, a growth factor produced by the liver. In fact, a human study found that subjects who took 150 milligrams of ursolic acid three times a day and strength trained experienced a rise in IGF-1. IGF-1, also known as insulin-like growth factor 1, an anabolic hormone that promotes muscle protein synthesis and cell proliferation. Your liver produces a certain amount of it naturally in response to growth hormone release, and anything that boosts IGF-1 will have an anabolic effect on muscle tissue.
Are Apples Good for Bone Health Too?
If ursolic acid boosts the release of IGF-1, it should also help preserve bone health. A study showed that ursolic acid stimulates osteoblasts, the cells that lay down new bone tissue. In addition, research shows that subjects who took ursolic acid gained muscle strength and lost body fat as well. Ursolic acid activates irisin and this, in turn, may increase thermogenesis. Irisin is a myokine, or small, biologically active protein produced by muscle cells, that activates or turns on metabolically inefficient brown fat. That’s favorable for fat loss. So, there’s some evidence that ursolic acid helps with fat loss as well as muscle gain. Sounds ideal, doesn’t it?
Apples and Ursolic Acid
Ursolic acid is found in varying quantities in a variety of plants. Unfortunately, most of the ursolic acid in apples is concentrated on the outer waxy coating of the apple – and you’d have to eat a lot of apples to turn on anabolic pathways. Estimates are that you’d have to eat around 11 apples with the skin intact to have an impact on muscle protein synthesis.
You can now buy ursolic acid supplements, but we don’t know what the long-term impact of taking ursolic acid as an isolated supplement would be. But, this substance does have the potential to slow age-related loss of muscle mass and bone density. In fact, we should see more research on it in the future as it appears to have anti-inflammatory, anti-viral, and, potentially, anti-tumor properties as well.
Eat Apples Anyway
You probably won’t notice a boost in muscle growth by eating an apple or two a day, but apples are one of the most satiating fruits, thanks to their high concentration of a water-soluble fiber called pectin. The pectin in apples aids in satiety and also blocks the absorption of cholesterol and fats. In fact, in a study carried out at Pennsylvania State University, participants who ate an apple prior to lunch consumed 187 fewer calories relative to those who didn’t munch on an apple.
Apples are also a good source of antioxidant compounds called flavonoids that help reduce inflammation. That’s important since so many health problems are fueled by low-grade, chronic inflammation. In fact, preliminary studies suggest that apple consumption is linked with a lower risk of developing a variety of health problems, including type 2 diabetes, cardiovascular disease, cancer, and, potentially Alzheimer’s disease and cancer. For example, in lab and animal studies, extracts from apple slow the proliferation of cancer cells and promote their destruction through a process called apoptosis.
Studies have also linked apple consumption with improvements in lung function and a reduction in the symptoms of asthma. For example, a study showed that apples were the only food linked with improvement in asthma symptoms in children. Although apples are relatively high in natural sugar, they don’t cause a rapid rise in blood sugar like processed foods that contain sugar. The naturally high fiber and polyphenol content of apples may actually reduce the blood sugar response.
The Bottom Line
Apples are a complex fruit that contains a variety of potentially healthful chemicals. The idea that ursolic acid in apple peels could boost muscle hypertrophy is an intriguing one. But, unless you plan on eating the peels of 11 or more apples daily, it probably won’t have a big impact on muscle strength or size. Still, there are lots of other reasons to eat apples. They’re nutritionally dense and loaded with fiber and phytonutrients. So, the next time you’re tempted to reach for a packaged snack, choose an apple instead!
References:
Nutrition Journal 2004 3:5. https://doi.org/10.1186/1475-2891-3-5.
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.
Adv Nutr. 2011 Sep; 2(5): 408–420.
WebMD. “Apples May Keep Asthma Away”