These Are the 10 Horrific Side Effects of Fasting and Losing Weight Too Quickly

You probably wish you could eat healthy today and wake up 10 pounds lighter tomorrow. You also probably know weight loss doesn’t work like that. Some people go to extremes, turning to fasting in search of supposed health benefits and magical weight loss miracles. Most of them don’t know they’re usually doing more harm than good.

Want to lose weight, but worried you’ll do lasting damage in the process? Here are all the ways fasting — and losing weight too quickly — can make you sick (page 8), increase your appetite (page 9), and more.

1. Your heart can’t take it

Digital illustration of Human heart

Your heart may suffer. | Hywards/iStock/Getty Images

Eating less (or nothing) to lose weight can actually put your life in danger, offsetting your body’s normal functions and rhythms. Fasting for long periods of time can also lead to electrolyte imbalances and irregular heartbeats.

Next: This can escalate beyond feelings of extreme hunger.

2.You’ll mess up your blood sugar

Man checking blood sugar level

This can be a pain to regulate. |

There’s an important reason people with Type 1 diabetes shouldn’t fast to lose weight. Fasting pauses or slows down the amount of glucose that enters your blood, which makes your blood sugar levels plummet. It could even drop dangerously low if you aren’t careful.

Next: Your brain won’t be happy with you.

3. You’ll feel confused

doubt and worry concept

This is a common side effect. |

When your blood sugar drops, one unfortunate side effect is that your brain won’t get the glucose (sugar) it needs to function properly. This can lead to a variety of issues, mostly confusion and headaches. It’s your brain’s way of saying, “Hey! Feed me now!”

Next: This could lead to a heart attack

4. You’ll probably lose muscle


You may not be able to workout like you used to. | Oatawa/iStock/Getty Images

If you lose weight too quickly, you run the risk of also losing muscle mass — which is a lot more dangerous than you might think. People who take fasting to the extreme are at an increased risk of having a heart attack, because the heart is just one big, very important muscle.

Next: No amount of caffeine will fix this problem.

5. You may feel tired

young man massaging his nose and keeping eyes closed

It may be hard to finish out your work day. |

Not feeding your body enough calories — your main source of energy — will leave you feeling fatigued. This can happen both in the short- and long-term. Some people find that eating small “meals” throughout the day produces much better results, if they choose the right foods.

Next: Trying to lose weight actually gets harder when you do it too quickly.

6. You’ll burn fewer calories


This goes against everything you’re working for. | Imtmphoto/iStock/Getty Images

When you eat fewer calories in an attempt to lose weight, you actually burn fewer calories as a result. Fasting for long periods of time slows down your metabolism, which is something many people try to combat to avoid weight gain.

Next: You probably never thought losing weight would affect this part of your body.

7. Your hair might start falling out

Young woman shows her gray hair

This is something no one wants to happen. | Manuel-F-O/iStock/Getty Images

Depriving yourself of food for too long could make your hair fall out. It doesn’t happen for everyone, but it’s another reason turning to fasting to lose weight might not be your best option after all. Your nails could also suffer the consequences of poor nutrition.

Next: This is probably the most inconvenient side effect of them all.

8. You might get sick more often

Sick woman cough in ved under blanket

Your immune system will suffer. | samotrebizan/iStock/Getty Images

Your body’s ability to fight off infections and disease-causing pathogens depends on the amount of nutrition you offer it. If you fast for too long, you could wreck your immune system. Nutritional deficiencies don’t happen overnight, but many people live with them and don’t know it.

Next: You might mess up an important hormone balance.

9. You might want to eat more

Hungry woman holding knife and fork

Bring on the food! | beer5020/iStock/Getty Images

If you suddenly and significantly decrease your food intake, you might actually notice an unexpected increase in appetite. This is because your body might produce less of the hormone that makes you feel full. Eating enough at regular intervals keeps levels of this hormone normal.

Next: Fasting doesn’t work for everyone.

10. It’s only temporary

Stressed n fat

Weight loss takes time and dedication. | Amazingmikael/iStock/Getty Images

Fasting isn’t an ideal weight loss solution if you’re trying to set long-term goals. Most people drop pounds quickly at first because they’re losing water weight, but hit a sort of plateau after awhile. It’s much better to lose weight the right way — slowly and sustainably — to create a foundation for a healthier life.

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