Let me start by saying that I love fruit. I often have it in my morning smoothie; I recommend it as an easy, portable and healthy snack; I include consumption of fruit in my top 5 nutrition tips; and I have said it’s a food that can always be eaten because it has lots of fiber, water and micronutrients.
As general statements, I still think all of that is true. And when I get into the nitty-gritty details about lots of foods (like gluten and dairy), I have to say that whether or not fruit is good for you depends on YOU.
Since you no doubt have heard lots of conflicting information about whether or not fruit is good for you (anybody heard that bananas are bad?!) and since I want you to have the complete story so that you can make the best decision for you, let’s talk about whether or not fruit is making us fat.
What are fruits, nutritionally?
Botanically, fruits are the product of any tree or other plant that contains seed and can be eaten as food. According to this definition, strawberries, avocados and tomatoes are all fruits. But nutritionally, they are handled differently by the body.
So, the nutritional definition of fruits is limited to produce that is sweet or tart, generally used as a snack or in dessert, and whose primary macronutrient is carbohydrate. This is why tomatoes and squash are vegetables, and avocado and olives are healthy fats, nutritionally speaking.
How are fruits digested?
As with most produce, fresh fruit is made mostly of water, with the amount ranging from 74% by weight in bananas to 92% in strawberries and watermelon. The remainder of the weight is made up of various macro-, micro- and phytonutrients. Given that our discussion is limited to produce that is considered fruit from a nutritional perspective, the order of these nutrients in descending order of quantity is:
- Digestible carbohydrates
- Fiber (which is indigestible carbs, as far as humans are concerned)
- Protein (0 – 1 g per serving, which makes it an insignificant source)
- Fat (typically only a trace of fat, which is negligible)
- Micronutrients (vitamins and minerals)
- Phytonutrients (such as antioxidants and polyphenols)
As discussed in depth in this other post, all carbohydrates break down into the monosaccharides glucose, galactose and fructose. Fructose is sometimes called “fruit sugar” because generally it is found in larger quantities in fruit, as compared with the amount found in vegetables or other carbohydrate containing foods like beans and bread.
As an interesting side note, if you’ve ever wondered why fruit is sweeter than other carbohydrate containing foods, this is why. With table sugar (sucrose = glucose + fructose) being considered perfectly sweet with a score of 100, fructose on its own receives a score of 110, while glucose rings in at 76 and galactose (or “milk sugar”) hits a score of only 60.
What foods are high in fructose?
The following fruits tend to be high in fructose, meaning that at least half of their carbohydrates are fructose:
Dried fruits, jams, jellies and fruit juices also tend to be high in fructose as their processing results in concentrated amounts of all carbohydrates.
As well, some vegetables are a bit higher in fructose than most of their counterparts, such as:
- Sugar snap peas
However, for many people, the majority of fructose in the diet is not from fruits or vegetables.
Most sweeteners contain fructose, sometimes connected to glucose and sometimes not. The more a sweetener is processed, the more likely it is to have fructose freely floating around. For example, table sugar (or sucrose) is glucose and fructose hooked together as a disaccharide, so there isn’t any free fructose in it and the ratio of glucose to fructose is 1-to-1.
On the other hand, high fructose corn syrup (HFCS) usually contains 55% fructose and 45% glucose, but the two monosaccharides are not linked to each other. This is an important distinction because sweeteners with free fructose do not need to be digested. The free fructose is quickly absorbed and taken to the liver where it may or may not be handled effectively (see the next section).
How is fructose handled in the body?
Fructose is carried from the intestine into the body by a special transporter that is primarily dedicated to bringing it into the body. Once in the blood stream, fructose travels via the portal vein to the liver. With normal amounts of fructose consumption, all of the fructose is converted to glucose in the liver where it can then be used the same as glucose from other sources.
When fructose consumption is excessive, some fructose will leave the liver without being converted to glucose, which means it will be found in the peripheral blood (the blood between the liver and the rest of the body). There is a dose response, meaning that the more fructose that is consumed, the more fructose will be found beyond the liver. The kidneys, brain, muscles and fat tissues have the ability to absorb fructose from the blood stream, although they aren’t very efficient at this process as it’s not generally how our bodies are intended to work.
As well, excess fructose increases the rate of lipogenesis (fat creation) in the liver, perhaps even more so than the intake of glucose or galactose. The increased creation of fat also results in increased insulin resistance, again at a higher rate from fructose over-consumption than from other monosaccharides.
What impact does high fructose intake have?
The impact of fructose in the body varies from person to person, and can include:
- Abdominal distress: The body can only absorb about 20 to 50 grams of fructose at one time. This may sound like a lot, but you can easily ingest 50 grams of fructose by drinking 25 ounces of soda sweetened with high fructose corn syrup. As such, a large intake of fructose can result in intestinal distress as the unabsorbed fructose travels further down the intestine and is consumed by your gut bugs. (Note that the amount of fructose required to cause problems varies from person to person, so it may take only 25 grams of fructose for you to experience symptoms.) Abdominal distress can appear as:
- Abdominal pain, and
- Increased fat production by the liver, which can lead to:
- Higher levels of blood triglycerides and LDL cholesterol
- Increased storage of fat in the liver, which can lead to non-alcoholic fatty liver disease (NAFLD), and
- Increased intra-abdominal fat (i.e., more fat around your middle).
- Increased insulin resistance, which can lead to many complications such as metabolic syndrome, type 2 diabetes and increased weight gain.
There are additional conditions that may be linked to fructose for some people. I say “may” be linked for “some” people because there are research studies that show fructose intake is related and others that show it isn’t related to:
- Increased blood pressure
- Increased uric acid production which can lead to gout
- Resistance to leptin (the hormone that tells your brain you are full and satisfied), and
- Insufficient suppression of ghrelin (the hormone that tells your brain you are hungry).
So, is fruit making us fat?
Honestly, it’s unlikely that fruit alone is making us fat. It is far more likely that our increased fructose consumption from foods and beverages sweetened with substances such as high fructose corn syrup are making us fat, increasing our risk for insulin resistance / type 2 diabetes / metabolic syndrome, and raising our blood levels of triglycerides and cholesterol.
That being said, there is some evidence that once a person’s metabolism is broken and/or the person is overweight that the fructose in fruit makes the situation worse.
As well, everyone is different and there are case studies of normal weight people with relatively healthy diets resolving their high triglycerides or high cholesterol by restricting their fruit intake to one serving per day.
As such, if you are struggling with any of the above symptoms and are looking for possible triggers, consider reducing or eliminating fruit for a period of time and see what the results are.
Oh, and no matter what your health situation, please stop consuming high fructose corn syrup and other “natural” sweeteners as much as possible. You will be doing your body, and especially your liver, a big favor!
— Cox CL, Stanhope KL, Schwarz JM, Graham JL, Hatcher B, Griffen SC, Bremer AA, et al. Consumption of fructose-but not glucose-sweetened beverages for 10 weeks increases circulating concentrations of uric acid, retinol binding protein-4, and gamma-glutamyl transferase activity in overweight/obese humans. Nutr Metab (Lond). 2012; 9(1): 68.
— Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism. 6th ed. Belmont, CA: Wadsworth Cengage Learning; 2013.
— Hofmann SM, Havel PJ. The good, the bad, and the unknown: Fructose and FGF21. Molecular Metabolism. 2015; 4(1): 1-2.
— Jacob A. Foods allowed for a fructose-restricted diet. In Healthy Eating. Accessed on October 21, 2015.
— Kuhnle G, Tasevska N, Khaw KT. Association between fructose, uric acid and blood pressure. The FASEB Journal. 2015; 29(1 Supplement): 736-21.
— Rebollo A, Roglans N, Alegret M, Laguna JC. Way back for fructose and liver metabolism: bench side to molecular insights. World Journal of Jastroenterology. 2012; 18(45): 6552.
— Spungen J. Bowes & Church’s Food Values of Portions Commonly Used. Lippincott Williams & Wilkins; 2005.
— Stanhope KL, Schwarz JM, Havel PJ. Adverse metabolic effects of dietary fructose: results from recent epidemiological, clinical, and mechanistic studies. Current Opinion in Lipidology. 2013; 24(3): 198.
— UVA Digestive Health Center. Low Fructose Diet. Accessed on October 21, 2015.