Is Fasting Worth the Hype?

diets weight management Dec 30, 2022

Katie Breazeale, MS, RD, LD


Are you thinking that Intermittent Fasting is your weight loss plan? Your friends are telling you how great it is, how much weight they’ve lost, and how easy it is. You just skip breakfast and then eat in you non-fasting window. That sounds so easy right. Just skip breakfast, eat when it is time to eat, and wah la weight loss. Too good to be true?


For some people maybe it is that amazing, for others there could side effects. Let’s look at the potential side effects and whether fasting is really the hype everyone is saying it is.


Side Effects

  1. Hunger- Sounds like a normal side effect to get hungry if you are fasting. You’re skipping meals and go long periods of time with nothing to eat. Of course you’re going to be hungry bordering on the edge of hangry. This side effect could decrease as your body adjusts to the fasting schedule.

  2. Headaches or lightheadedness- Is it from the lack of caffeine or the blood sugar from not eating? These are common reasons why the headaches start to come. Long term or goes away with time? Your body could adjust to the lack of caffeine, but the low blood sugar is up for debate. Low blood sugar can also cause lightheadedness, dizziness, or nausea.   

  3. Digestive Problems- Problems could include constipation, nausea, bloating, or diarrhea. Constipation is one of the most common symptoms due to the decreased consumption of water and fiber. The bloating and diarrhea can occur from your new diet and the changes you may be making to intermittent fast.

  4. Mental Changes- Have you noticed when you’re hungry you get cranky? This is a side effect of fasting. You’re skipping meals and getting irritable in the process. Lack of calories can also lead to brain frog and decreased concentration.  

  5. Fatigue- This side effect is one of the most unavoidable of the symptoms. Lack of calories or eating foods that are not nutritionally dense but higher in fat can lead to fatigue. Now add in physical activity- light or athlete level is going to be a challenge. You are missing necessary calories for fueling, replenishing glycogen stores, and building muscles.

  6. Sleep Issues- Fasting can a dip in the sleep hormone melatonin which plays an important role in your sleep patterns. Limiting your calories may also trigger a spike in cortisol, the hormone associated with stress. Cortisol is also responsible for regulating blood sugar levels, metabolism, and inflammation. Too much cortisol can reduce sleep quality and make it difficult to fall asleep.

  7. Bad Breath- A surprising side effect from fasting. This is caused by lack of salivary flow and the rise of acetone in your breath. Fasting causes your body to use fat for fuel. Acetone is a by-product of fat metabolism thus increasing in your blood and breath when you are fasting. Dehydration can cause dry mouth and may also lead to bad breath.

  8. Dehydration- This commonly happens while fasting due to the lack of regular meal and snack times all day. Even though you’re fasting from food you can still enjoy water during your fasting window.

  9. Malnutrition- People think of malnutrition typically as being underweight and with little to no fat or muscle. Malnutrition is more than that. Restricting nutrients and becoming deficient in certain food groups, vitamins, or minerals play a roll in your nutrition status along with your health.

  10. Hormonal Imbalances- Too restrictive of a calorie amount can affect a female’s menstrual cycle. Sudden weight loss can affect the hormone cycle. 

Bonus! Unhealthy Eating Behaviors and Food Obsessions- Unhealthy eating behaviors can form from fasting. Binge eating is one behavior that can form. Think about it, you’re hungry from fasting and you overeat during your non-fasting window. Another behavior could be food obsessions. Frequent thoughts about when you can eat, what you’re going to eat, or how many calories you’re eating a day. These behaviors can lead to a disgruntled relationship with food.


Is fasting safe? For most people fasting is safe. But…. there is always a but, there are individuals who would benefit from avoiding a fasting diet. This list is not going to list off every medical situation.

  • People who are pregnant or breastfeeding

  • Young children and teens

  • Older adults who experience weakness

  • People with immunodeficiencies

  • People with current or past eating disorders

  • Diabetics

  • People with dementia

  • Those with a history of traumatic brain injury or post concussive syndrome


There’s more to fasting than just skipping breakfast. And like all diets it has its pros and cons. Keep in mind there is more than one way to lose weight. Talking with a dietitian can help you create a plan for proper weight loss and learn healthy behaviors for positive change. 

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