Most fruit is not considered an acceptable food on the keto diet. Fruit is too high in carbohydrates and fructose/sugar, which spikes blood sugar and insulin.
The “no fruit on keto” rule exception is berries, which are acceptable in small quantities. Here is the net carbohydrate count of berries per cup:
- Raspberries 5
- Blackberries 5
- Strawberries 6
- Blueberries 12
If you thought that fruits were the perfect health food read on.
First of all, let me clarify, this is not an anti-fruit rant. Fruits do exactly what they were intended to do. They have historically been used to fatten up man and animals before winter.
Fruits were intended to be eaten only seasonally when they became ripe in the fall. Bears eat a lot of berries to increase their fat stores before hibernation.
Bears begin eating in the spring by gorging carbohydrate-rich berries and other foods to put on weight and can gain approximately 20-30 pounds of body fat per week.
Bears live off of their own fat while hibernating. Kind of similar to a human eating a ketogenic diet and fasting.
On a side note: many people worry about increased cholesterol when they go on a Ketogenic Diet. Hibernating bears also have high cholesterol levels.
Due to the fact they live off their own fat while hibernating, a bear’s cholesterol levels are more than twice what they are in summer. Interestingly though, a bears show no signs of hardening of the arteries or the formation of cholesterol gallstones.
Maybe human medical doctors can learn something from bear physiology when they are hibernating.
But I digress, back to the keto diet and fruit.
The primary energy substrate in fruit is fructose. Three recent clinical studies, which investigated the effects of consuming sucrose or high-fructose corn syrup clearly displayed that high consumption of these sugars increases the risk factors for cardiovascular disease and metabolic syndrome.
Metabolic syndrome, if untreated usually leads to type 2 diabetes. The ketogenic diet has been shown to reverse metabolic syndrome. Here is a good explanation of the keto diet if you’re not sure what it’s all about.
Fruit can contribute to a fatty liver
The liver stores energy as liver glycogen and frequent snacking and/or a high carbohydrate diet keep the liver constantly full, so when it encounters fructose it turns it to fat and triglycerides and accumulates fat inside the liver itself.
The MRI of a fatty liver usually shows that is enlarged. That’s one of the ways a ketogenic diet heals a fatty liver, it empties the liver of liver glycogen and forces it to burn its fat inside the liver.
But wait, the fructose found in fruit is natural sugar, that’s good for you right?
That’s a complicated question. The problem with fructose is that it must be metabolized by the liver and isn’t used for immediate energy by our cells.
Like any simple sugar, it’s a toxin in high amounts and the liver has to metabolize it into fat and stores that fat in the liver and creates triglycerides.
The role of fructose inside the liver is complex. One of the negative by-products is raising triglycerides and uric acid.
Excess fructose also increases free radicals and inflammation, which can oxidize, glycolate the cholesterol and contribute to cardiovascular disease.
Fruit and the keto diet are not a good combination.
On the ketogenic diet the liver is needed to make ketones. If the liver is full of fructose it won’t make ketones. All is not lost though, if you have fallen out of ketosis because you ate fruit or another sugar:
Here is a technique to get back into ketosis in 24 hours.
Too much fructose can also cause triglycerides to build up in liver cells and damage liver function. Triglycerides released into the bloodstream can contribute to the growth of fat-filled plaque inside artery walls.
Free radicals (also called reactive oxygen species) can damage cell structures, enzymes, and even genes.
I recommend an excellent lecture available on Youtube by Robert H. Lustig, MD, UCSF Professor of Pediatrics in the Division of Endocrinology called: Sugar: The Bitter Truth.
Fructose is known as a simple sugar because it is a single sweetening molecule known as a monosaccharide. Fructose is up to twice as sweet as sucrose (table sugar). It’s not the exact same thing as high fructose corn syrup.
Stay away from high fructose corn syrup
High fructose corn syrup (HFCS) contains 42-55% fructose and 45-58% glucose. HFCS is commonly found in soda pop and other sweetened products and in this day and age, no one considers HFCS a healthy sweetener.
Excessive fructose is toxic to the liver in a similar way that alcohol is. High fructose corn syrup and corn gluten can be converted into ethanol alcohol in 3-5 days.
The other problem with fructose is that it suppresses the hormone leptin. Leptin is the hormone that signals to you the feeling that you are satiated (full) and don’t need to eat anymore.
The study referenced here on PubMed show a 30% reduction in leptin after eating a fructose sweetened meal. The hormone leptin gives you satiety and makes you feel full.
The study summarizes that “Diets high in fructose consumption could lead to increased caloric intake and ultimately contribute to weight gain and obesity.”
Additionally, researchers at Yale discovered that leptin was released in lesser amounts when people consumed fructose as opposed to glucose. So if you snack on a banana, for example, you will still be hungry and probably want to eat something else.
A banana raises blood sugar more than a chocolate bar (video)
All fruit sugar (fructose) works the same in the body, whether it comes from corn (syrup), sugar cane, beets, strawberries, bananas, or honey. The ratios are just different.
For example, a cup of chopped tomatoes has 2.5 grams of fructose, a can of regular soda pop contains 26 grams, and a super-size soda has about 63 grams. Even honey isn’t as healthy as people think. It (honey) has about the same fructose/glucose ratio as high fructose corn syrup.
Eating fruit and trying to stick to a keto diet will be next to impossible. Your liver will remain full of glycogen and you will rarely be in fat burning state of ketosis.
The problem is we eat fruit too much and too often.
The human species developed on earth we primarily ate the fruit in the fall when fruit became ripe, we didn’t eat it all year long.
Remember the story about the bear. We didn’t hibernate, but humans needed to fatten up before the winter, so that way if we ran out of food in the winter, we could live off of our accumulated fat stores.
The fruit became ripe in the fall, just when we needed it. We only ate fruit seasonally. Without fruit in the fall, the human species might have perished like the dinosaurs.
For thousands of years, we consumed approximately 16–20 grams per day. Now, we are seeing a huge increase in fructose consumption of about 85–100 grams of per day.
The average middle-aged adult never stops eating long enough to empty the liver of its glycogen stores, so the excess fructose is converted to fat and triglycerides.
Then there are those that fit into the category of a group of people that would do better without fruit.
People that should limit fruit intake have:
- Fatty liver disease
- IBS (irritable bowel syndrome)
- Overweight or overfat
- Type 2 diabetic
- Metabolic syndrome
- Insulin resistant
However, fruit is not all bad
OK, so fruit has evil fructose, but it has other beneficial nutrients also. To come to the rescue of fruit, I will contend that fruit does have a lot of amazing antioxidants and other nutritional benefits.
Fruit contains, fiber, phytochemicals, micronutrients, flavonoids, anthocyanins, carotenoids, vitamin C, folate and some fruits are high in prebiotics. Also, fructose doesn’t have as high of a glycemic load as other sugars, so it doesn’t create as big of an insulin spike.
If you eat the entire fruit with the skin and fiber it is much more healthy than a candy bar. Of course, if you drink “fruit juice” you are removing all the good part of the fruit and leaving mostly the fructose.
Remember my comparison of fructose to ethanol? If you wouldn’t give your children vodka, you shouldn’t give them fruit juice.
Active kids can eat fruit without any problems
For the general, healthy population, eating fruit occasionally is fine. Some fruits are better than others, remember over-ripe fruit has more sugar in it than ripe fruit.
Fruit would benefit and active people with healthy body weight and healthy metabolism would do just fine by eating fruit in moderate amounts, occasionally.
Don’t peel that apple and only partially peel that orange before you give it to your child. The white fleshy material between the orange and the skin is called the pith.
The apple skin and the orange pith contain citrus pectin which has a ton of nutritional benefits including prebiotic fiber that will help your child’s digestion and strengthen his immune system.