Updated: Sep 29, 2020
Your metabolism refers to all the chemical reactions that occur within your body. Having a fast metabolism means that your body burns more calories. On the other hand, having a slow metabolism means that your body burns fewer calories, making it more difficult to maintain or lose weight. Some foods may increase your metabolism. But how does junk food affect it? This article explores whether processed foods slow down your metabolism.
What Is Junk Food?
Junk food refers to highly processed foods that are generally high in calories, refined carbs and unhealthy fats. They're also low in filling nutrients like protein and fibre. Some examples include french fries, potato chips, sugary drinks and most pizzas. Junk food is widely available, cheap and convenient. Also, it's often heavily marketed, especially to children, and promoted with misleading health claims.
While it is tasty, it is usually not very filling and is easy to overeat. Interestingly, junk food may also affect your brain in a very powerful way, especially when consumed often and in excessive amounts. It may trigger a massive release of dopamine, a neurotransmitter that helps control your brain's reward and pleasure center. When your brain is flooded with dopamine in such unnatural amounts, it can cause food addiction in some people
It Takes Less Energy To Digest Junk Food
It requires energy to digest, absorb and metabolize the food you eat. This is referred to as the thermic effect of food (TEF), and it generally accounts for around 10% of your daily energy expenditure. Metabolizing protein in food requires a lot more energy than metabolizing carbs or fat. In fact, eating a high-protein diet may cause your body to burn up to 100 more calories per day.
Furthermore, the degree to which foods are processed affects the TEF. It will generally be higher when you consume whole foods made of complex nutrients, compared to refined, processed junk foods. To investigate this, one small study in 17 healthy people compared two sandwich meals that differed in their level of processing, but not their macronutrient composition or calorie content.
The study found those who consumed a whole grain sandwich with cheddar cheese burned twice as many calories digesting and metabolizing the meal than those who ate a sandwich made with refined grains and processed cheese. While this study was small, the results indicate that processed food requires less energy to digest and metabolize than whole foods. This leads to fewer calories burned throughout the day, making weight loss and maintenance more difficult.
Junk Food May Cause Insulin Resistance
Insulin resistance is when your body's cells stop responding to the hormone insulin. This can lead to higher blood sugar levels. Insulin resistance is a major risk factor for metabolic syndrome, type 2 diabetes and other serious diseases. The consumption of processed foods has been associated with an increased risk of insulin resistance.
A small study in 12 healthy men reported changes in the ability of skeletal muscle to process glucose after only five days on a diet rich in fatty processed foods. The researchers concluded that a diet comprised of high-fat junk foods may lead to insulin resistance in the long term. Furthermore, the results of a 15-year study indicate that your risk of developing insulin resistance may double when you visit a fast food restaurant more than twice per week, compared to less frequently. This implies that eating junk food on a regular basis may promote insulin resistance.
Sugar-Sweetened Beverages May Slow Down Your Metabolism
Of all the junk foods out there, sugary drinks may very well be the worst for your body. When consumed in excess, they may contribute to all sorts of health problems, including obesity, heart disease, metabolic syndrome and type 2 diabetes. These issues are mainly attributed to their high levels of fructose, a simple sugar primarily metabolized by the liver. When you consume a lot of fructose, the liver may become overloaded and turn some of it into fat.
Sugar-based sweeteners like table sugar (sucrose) and high-fructose corn syrup are around 50% fructose and commonly found in sugary drinks. When consumed in large amounts in the form of added sugars, fructose may alter fullness signals, impair the response of the "hunger hormone" ghrelin after meals and promote fat storage around the belly. Additionally, it may slow down your metabolism.
In one study, overweight and obese people consumed drinks that were sweetened with fructose and provided 25% of their daily calorie intakes. During a 10-week period, they experienced a significant drop in resting energy expenditure. This suggests that the fructose in sugary drinks may decrease the number of calories you burn, at least when consumed in excess.
It's Not Only About The Calories
Decreasing your calorie intake is important if you want to lose weight. However, the calorie content of your food isn't the only thing that matters. The quality of the foods you eat is just as important. For example, eating 100 calories of french f