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Save your liver: Sweeten your holidays with fruit

December 19, 2021 at 4:00 a.m.

The holidays are a time in which most people consume a few more sweets than usual, which could lead to feelings of guilt come January. Sugar gets a bad rap these days, but I want to make it clear that not all sugar is bad for you. The confusion lies in the distinction between naturally occurring sugars found in fruits and vegetables, and "added sugars" found in processed foods. Though these sugars may be chemically similar, our bodies know the difference.

Fructose and fatty liver disease

If you've ever had corn on the cob, you know that it's not typically eaten for dessert. Most people consider corn on the cob to be a savory side dish. They season it with salt and pepper. But it contains small amounts of naturally occurring fructose that is packaged tightly inside cell walls in the corn.

In the 1950s, food manufacturers figured out a way to strip all the fiber, water, vitamins, minerals, and other essential nutrients out of corn in order to make a sweetener that would be cheaper than sugar. They isolated the fructose in corn and made it into a cheap, sweet syrup we now call high fructose corn syrup.

High fructose corn syrup is rapidly metabolized by the liver using a similar pathway as alcohol metabolism. This causes something called de novo lipogenesis in the liver, meaning the liver starts putting on fat.

Fatty liver disease used to be something only seen in people who drink a lot of alcohol. But after high fructose corn syrup was introduced, children and people who don't drink alcohol at all started showing up in doctors' offices with fatty livers that look just like those seen in people who drink a lot of alcohol.

This led to the coining of the term nonalcoholic fatty liver disease. Johns Hopkins Medicine now estimates that as many as 20% of Americans have nonalcoholic fatty liver disease even though many of them don't know it yet.

That's because the symptoms of nonalcoholic fatty liver disease can be vague or there could be no symptoms at all. The most common symptom is tiredness, which many people with undiagnosed NAFLD may attribute to school or job stress.

A blood test of liver enzymes alanine transaminase (ALT) and aspartate transaminase (AST) can give an indication of liver function. These enzymes are usually tested as part of a routine blood test called a complete metabolic panel (CMP).

A slight elevation of one or both of these enzymes could indicate fatty liver disease, while a large elevation could indicate something even more serious going on with the liver. An abnormal liver enzymes test is usually followed up with an abdominal ultrasound to look at the size of the liver and look for signs of fatty tissue, inflammation, or scarring.

Free fructose vs. fructose in fruits and vegetables

There is clear evidence that processed foods containing added fructose or "free" fructose (usually in the form of high fructose corn syrup) can directly contribute to the development of nonalcoholic fatty liver disease.

Individuals consuming just one soft drink per day have a higher incidence of nonalcoholic fatty liver disease and metabolic syndrome than people who drink less than one soft drink per day.

But is there any evidence that the naturally occurring fructose in fruit could cause fatty liver? Should you limit the amount of fruit in your diet or only choose fruits that are low in fructose?

Epidemiological studies have found that people who eat the most fruit have the lowest incidence of nonalcoholic fatty liver disease. Other studies have found whole fruits have liver-protective properties and that the small amounts of naturally occurring fructose in fruit help prevent insulin resistance and fatty liver.

For instance, in one study on obese individuals who had been diagnosed with metabolic syndrome and nonalcoholic fatty liver disease, those who ate the most fruit showed the most improvements in the fatty liver index, the hepatic steatosis index, NAFLD liver fat score, and liver enzymes.

One double-blind, placebo-controlled study assigned people living with uncontrolled type 2 diabetes to a group that received either 7.5 grams of fructose or maltodextrin supplementation three times a day, with meals. After two months, the group that received the small doses of fructose had significantly lowered their A1c.

High fructose corn syrup and weight gain

Insulin resistance and fatty liver disease aren't the only health concerns that high fructose corn syrup and processed junk foods have been linked with in epidemiological and clinical research studies.

High fructose corn syrup has long been suspected for fueling the obesity epidemic, but the exact mechanism has remained a mystery until recently.

One hypothesis was that fructose stimulates ghrelin (a hormone produced in the stomach that stimulates appetite) and suppresses leptin (a hormone produced by fat cells that makes you feel full). Even though this hypothesis is touted as a scientific fact by people who promote a low carb or ketogenic diet, research studies still fail to demonstrate this phenomenon.

However, in August, a study published in the renowned medical journal Nature found that high fructose corn syrup can increase the surface area of the gut and enhance absorption of calories from food. When you absorb more calories from the food that you eat, you're more likely to gain weight.

Of course, this study was done on mice. We have yet to see whether high fructose corn syrup enhances calorie absorption in humans, but it's highly likely that these same findings will be seen in human studies.

But high fructose corn syrup is not the same thing as the naturally occurring fructose in fruit. While high fructose corn syrup sweetened beverages are strongly linked with weight gain, fruit is strongly linked with weight loss and having a low body weight.

Because fruit is primarily made up of different types of sugars, including sucrose, glucose, and fructose, but actually has an anti-obesity effect, researchers sometimes refer to this as the "fruit paradox."

A number of clinical studies have found that fruit consumption is inversely linked to weight gain, meaning that people who eat the most fruit tend to have the lowest body weight. People who eat the least fruit tend to be obese. But when obese people increase their fruit consumption, they lose weight.

The fiber, micronutrients, and polyphenols in fruit may promote weight loss by decreasing the surface area of the gut and reducing calorie absorption from food. In other words, it has the opposite effect on the gut that high fructose corn syrup has.

It's important to note that fruit juices and canned fruits (which often have high fructose corn syrup added to them and are lacking in fiber) are usually linked with weight gain rather than weight loss.

This is why I recommend eating fresh, whole fruits as opposed to fruits that have been overly processed or sweetened with added sugars.

How to choose the best-tasting fruit

Fruit that is in season is inherently going to taste more fresh and flavorful than fruit that has either been shipped from another country or has been in cold storage for up to a year. During the winter months, look for oranges, clementines, mandarins, grapefruits, pomegranates, pears, apples, persimmons, and honeydew melons.

Tropical fruits such as papayas, bananas, black sapote, pineapple, avocado, cherimoya, star apple, rollinia, sapodilla, soursop, guava, coconut, passion fruit, cacao (chocolate), and jackfruit are also harvested during the winter months in south Florida. These sometimes hard-to-find fruits can be a real treat, especially on cold days when you're craving something with a rich flavor.

Luckily you don't have to live in the tropics in order to get farmers market quality tropical fruits shipped to your doorstep the day after being harvested. Simply go online to MiamiFruit.org, add the fruits you want to your shopping cart, and use coupon code DRJAMIE at checkout for a sweet deal.

For more information, please send an email to [email protected]

SOURCES

Jensen, Thomas et al. "Fructose and sugar: A major mediator of nonalcoholic fatty liver disease." Journal of hepatology vol. 68,5 (2018): 1063-1075. doi:10.1016/j.jhep.2018.01.019

Nseir, William et al. "Soft drinks consumption and nonalcoholic fatty liver disease." World journal of gastroenterology vol. 16,21 (2010): 2579-88. doi:10.3748/wjg.v16.i21.2579

Kim S, Shin S, "Fruit and vegetable consumption and nonalcoholic fatty liver disease among Korean adults: a prospective cohort study." J Epidemiol Community Health 2020;74:1035-1042.

Cantero, Irene et al. "Fruit Fiber Consumption Specifically Improves Liver Health Status in Obese Subjects under Energy Restriction." Nutrients vol. 9,7 667. 28 Jun. 2017, doi:10.3390/nu9070667

Vaisman, Nachum et al. "Catalytic amounts of fructose may improve glucose tolerance in subjects with uncontrolled non-insulin-dependent diabetes." Clinical nutrition (Edinburgh, Scotland) vol. 25,4 (2006): 617-21. doi:10.1016/j.clnu.2005.11.013

Zhiping Yu, Joshua Lowndes, James Rippe. "High-fructose corn syrup and sucrose have equivalent effects on energy-regulating hormones at normal human consumption levels."

Nutrition Research. Volume 33, Issue 12, 2013, Pages 1043-1052, ISSN 0271-5317, https://doi.org/10.1016/j.nutres.2013.07.020

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