Is intermittent fasting good for you? Myths versus facts

Wondering if intermittent fasting is for you? Here’s what the science says.

The practice of fasting has been around for millenia. Before farming was widespread, ancient hunter-gatherer societies didn’t have food readily available as we do today, so we evolved to be able to function without eating for longer periods than we typically do. 

Intermittent fasting is a more recent health trend that has grown popular in recent years. Advocates tout its many benefits and use intermittent fasting to lose weight, boost wellbeing, and simplify their lifestyle. But what do scientists and medical experts have to say on the matter? Does intermittent fasting work for weight loss? In this blog article, we take a close look at the latest research on intermittent fasting. Here’s what we cover: 

  • Intermittent fasting is a dieting strategy that restricts eating to specific hours or days. Studies show that it is effective for weight loss.
  • Evidence finds a wealth of health benefits to intermittent fasting, including the prevention of chronic conditions. But experts agree that more research is needed to determine the long-term impacts of fasting before officially recommending it.
  • Intermittent fasting isn’t safe for everyone and may have some negative side effects. Consult your doctor before trying it.

What is intermittent fasting? 

Most diets, like the paleo, keto, and Mediterranean diets, center around what to eat, limiting certain foods to promote weight loss and overall health. The intermittent fasting diet is unique in that it focuses not on what but when to eat – confining your eating window to certain times of the day or days of the week. 

There are several ways to go about it. Three common approaches to an intermittent fasting schedule include: 

  • 16-hour fast: Limiting eating to 8 hours per day and fasting for 16 hours. In this approach, people often skip breakfast and aim to eat dinner no later than around 8pm.
  • 5:2 diet: Fasting two days per week (or limiting food intake to 500 calories) and eating normally for the rest of the week.
  • Alternate-day fasting: Following a regular eating pattern one day and fasting the next. Fasting days can involve one small meal under 500 calories. 

During days and times when you are not fasting, you can eat what you want, but it’s recommended to keep a healthy, balanced diet. While fasting, water and calorie-free beverages, like unsweetened tea and black coffee, are allowed.

How does intermittent fasting work? 

Here’s what happens during intermittent fasting: when you don’t eat for an extended period, your body stops using glucose stored in the liver for energy. Instead, it switches to ketones, which are molecules stored in fat. Researchers refer to this process as “metabolic switching.” So, intermittent fasting works by burning fat, thus promoting weight loss. 

Enhanced activity of ketones in the bloodstream kickstarts cellular mechanisms which influence the body in a number of ways. Research has found numerous benefits of intermittent fasting, from chronic disease prevention to improved brain function. 

What the science says: benefits of intermittent fasting

In recent years, many scientific studies have examined how intermittent fasting influences health and wellbeing. Let’s dive into the evidence. 

It boosts heart health.

Research finds that intermittent fasting positively affects blood pressure, HDL cholesterol, and other measurements linked to cardiovascular health. A 2018 randomized clinical trial of 112 obese adults showed that both intermittent fasting and continuous calorie restriction improved risk factors for heart disease. 

It lowers insulin resistance. 

Evidence published in the American Journal of Clinical Nutrition found that when adults with a normal body mass index (BMI) followed an alternate-day fasting schedule for three weeks, insulin levels dropped by 50-60% on the fasting day. 

Johns Hopkins cites research that intermittent fasting can benefit people with type 2 diabetes by promoting weight loss, lowering fasting glucose, fasting insulin, and leptin levels, and decreasing the body’s resistance to insulin.

It may help prevent chronic illnesses. 

A 2017 review finds that intermittent fasting can counteract chronic, age-related diseases like diabetes, heart disease, and some neurological disorders, including Alzheimer’s, Parkinson’s, and stroke, according to studies on rats and mice. For conditions related to inflammation, intermittent fasting may be more helpful than other dieting strategies.

It can improve brain function.

Multiple studies have found benefits of intermittent fasting for mental health and brain function: it can increase stress resilience, raise resistance to injury and diseases that impact the brain, and improve mood and memory. 

It might increase physical performance. 

In a 2018 study on mice, researchers found that those who followed an alternate-day fasting plan had more running endurance and efficient metabolism. 

It may help with hormonal conditions like PCOS. 

Polycystic ovary syndrome (PCOS) is one of the most common hormonal conditions among reproductive-age females worldwide and a leading cause of infertility. Recent research from 2021 and 2022 discovered that intermittent fasting regulated the menstrual cycle in over 73% of females, decreased androgen hormones, improved insulin resistance, lowered chronic inflammation, and boosted fertility. 

So far, science has shown very promising effects of intermittent fasting on health. However, the Academy of Nutrition and Dietetics, Harvard Medical School, and the U.S. National Institute on Aging agree that more research is needed to find the real benefits. 

Many studies involved small groups of human participants or animals over a short timeframe, so findings may not apply to the general population. The long-term health impacts of intermittent fasting and the possible risk of nutritional deficiencies still need to be determined. 

In a 2018 study on mice, researchers found that those who followed an alternate-day fasting plan had more running endurance and efficient metabolism.

Intermittent fasting for weight loss

Research finds that, yes, intermittent fasting works for weight loss. It has about the same outcome as traditional calorie restriction. This makes sense because reducing how many calories you consume should help your waistline, whether you do that by skipping certain meals or eating foods containing fewer calories.

The randomized clinical trial of 112 obese adults mentioned above found that participants in the intermittent fasting and overall calorie restriction groups lost between 8 and 9 kilograms (kg) over one year. There were no significant differences in weight regain or heart health markers between the two groups. Another randomized clinical trial from 2022 found that a 16-hour fast had the same benefits for weight loss as traditional calorie restriction. 

An upside to this dieting strategy is that it allows a degree of flexibility: You can choose your intermittent fasting schedule and you don’t need to cut out specific food groups. But of course, eating lots of processed and fatty foods while practicing intermittent fasting is likely to prevent you from reaching your target weight. If you’re someone who tends to snack a lot at night or eat a late dinner, intermittent fasting may help you achieve your health goals by setting specific times for meals.

The bottom line here is that decreasing your overall caloric intake can promote weight loss, and may help lower the risk of chronic disease. But until more research is done on the impact of intermittent fasting over time, major health organizations do not officially recommend it as a weight loss strategy. 

How to use blood testing to evaluate the effects of your fast

Before you start an intermittent fasting regimen or if you want to do a check-in in between, a blood test can be helpful tool to determine your current health status or progress over time. Because fasting can cause changes to your metabolism and other biological processes, taking a look at your biomarkers will give you more insights about how a fasted state impacts your unique biology.

Markers that are especially important include:

  • HbA1c: This shows the average blood sugar level over the last 2 to 3 months. About half of the contribution comes from the last 30 days. It helps indicate the risk for pre-diabetes and diabetes.
  • Cholesterol markers: LDL or “bad” cholesterol, HDL or “good” cholesterol, and triglycerides are all types of lipids – wax-like fats in the blood whose levels indicate heart health.  According to a 2022 meta-analysis, intermittent fasting has been shown to effectively reduce levels of total cholesterol, LDL cholesterol, and triglycerides as well as improving insulin resistance in patients with impaired metabolic function.
  • Ketones: Ketones are acids produced in the liver when the body is in a state of ketosis. Depending on their unique characteristics and metabolic baseline, some people can enter a state of ketosis during intermittent fasting, even if they don’t follow a keto diet.
  • CRP: C-reactive protein is a key marker to measure inflammation and one of the most important markers of cardiovascular disease risk. According to a 2020 meta-study, intermittent fasting may reduce CRP levels, particularly in people who have excess weight or obesity. 
  • Leukocytes: White blood cells are the defenders of the body and support the immune system by fighting off infection and promoting healing. A University of Southern California study found that fasting lowers white blood cell counts which triggers the immune system to start producing new ones, boosting the immune function.

Potential downsides of intermittent fasting

If you’re interested in trying intermittent fasting, it’s helpful to be aware of some possible pitfalls or side effects before you start. 

First, hunger pangs on days you are fasting can make it harder to stick to an intermittent fasting schedule. Researchers found that people following an alternate-day fasting pattern were more likely to drop out of the study than those who limited overall daily calories (38% versus 29%). Doing a 16-hour fast or eating one small meal on days you are fasting may make it easier to stay the course.

Second, going for a long time without food (one to three days) is not good for you and can harm your health. In fact, starvation may counteract weight loss by increasing fat storage in the body. 

Third, intermittent fasting can cause some side effects. Besides hunger, you may experience fatigue, irritability, sleeping problems, nausea, and headaches. But the Mayo Clinic states that these symptoms typically disappear within about a month. Males may experience lower libido and adverse effects on metabolic health due to decreased androgen hormones, research finds

It’s also possible for fasting to lead to unhealthy eating behaviors like binging or undereating, so keep an eye on how it affects your relationship with food if you try it.

Who shouldn’t try intermittent fasting? 

Some groups of people should avoid intermittent fasting because it may pose a health risk. These include:

  • pregnant and breastfeeding or chestfeeding people 
  • people with type 1 diabetes
  • children and teens under the age of 18
  • people with kidney stones
  • people with gastroesophageal reflux
  • people with a history of eating disorders
  • people prescribed medication that needs to be taken with regular food

Fasting can affect people differently and there’s no such thing as one-size-fits-all when it comes to managing health. You are unique, and so is your body. Consult your doctor before starting an intermittent fasting diet to make sure it’s safe for you, particularly if you have an underlying medical condition. 

You may also want to meet with a registered dietitian nutritionist to create a meal plan and ensure you meet your nutritional needs. And be sure to listen to the signals from your body. If you notice that intermittent fasting severely impacts your mood or daily life, it may not be the right dieting plan for you. 

The bottom line

Intermittent fasting has significantly grown in popularity in recent years. Research finds many potential health benefits, but experts agree that more research is necessary to discover how it affects the body over the long term.

So is it the holy grail of dieting strategies? Probably not, because evidence shows that it has about the same effect on weight loss as traditional calorie restriction. If you want to try intermittent fasting for weight loss, it’s best to talk to your doctor first and stay tuned in to the signs from your body to monitor its effects.

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