Calculators

Intermittent Fasting Calculator

By Ted KallmyerUpdated April 16, 2024

Intermittent fasting is a dietary pattern involving alternating fasting and eating periods.

Age

Biological Sex

Weight

Height

Activity Level ?

Method

Tracking and managing your IF diet

To ensure you lose fat and not muscle, weigh yourself with an advanced scale like Renpho. This will show your body composition, rather than just weight.

To log your eating, use the Simple app. It eliminates the drudgery of tracking your meals (just talk to the app or take a photo).

Intermittent Fasting Methods

The most popular approaches include the following:

  • 16/8 method
    Fast for 16 hours and eat within an 8-hour window each day.
  • 5:2 diet
    Eat normally for five days and reduce calorie intake to 500-650 calories on two non-consecutive days.
  • Alternate-day fasting
    Fast every other day or reduce calorie intake to 25% of normal intake on fasting days.

This sounds complicated – how do I follow a plan?

Use Simple.

This app allows effortless scheduling (for any method you choose). 👇

How does Intermittent Fasting aid weight loss?

Intermittent Fasting (IF) can be a powerful tool for weight loss, as it reduces calorie intake and improves the body’s ability to burn fat.

It’s effective for short-term and long-term weight loss and especially helpful if you struggle with traditional calorie-restriction diets.

IF helps preserve muscle mass and increase metabolism, leading to sustainable weight loss.

16/8 Method

The 16:8 method involves fasting for 16 hours and eating within an 8-hour window each day.

For example, you might eat between noon and 8 pm and fast for the remaining 16 hours.

This time-restricted method is the easiest to follow and can be incorporated into most lifestyles.

5:2 Diet

This method involves eating normally for five days and reducing calorie intake to 500-600 calories on two non-consecutive days.

For example, you might fast on Mondays and Thursdays while eating normally on the other days of the week.

This method is a great starting point for trying out intermittent fasting.

Alternate-Day Fasting

This method involves fasting every other day or reducing calorie intake to 25% of normal fasting days.

Here’s an example:

Day 1 (Feeding Day):

  • Breakfast: Scrambled eggs with spinach and tomato, whole-grain toast, and a small fruit
  • Snack: Greek yogurt with berries
  • Lunch: Grilled chicken salad with mixed greens, cucumber, and avocado
  • Snack: Apple with almond butter
  • Dinner: Baked salmon with roasted vegetables and quinoa
  • Snack: Dark chocolate

Day 2 (Fasting Day):

  • Breakfast: Black coffee or tea
  • Snack: Water or herbal tea
  • Lunch: Vegetable broth or miso soup
  • Snack: Water or herbal tea
  • Dinner: Salad with mixed greens, tomatoes, and a small amount of protein (such as chicken or tofu)
  • Snack: Water or herbal tea

On fasting days, it’s important to stay hydrated.

Time-Restricted Eating (TRE)

The most popular method of time-restricted eating is the 16:8 method.

However, this can be customized to any format, such as eating only between 7 am and 1 pm.

Example plan:

  • 7 am: Wake up and have a cup of coffee or tea.
  • 9 am: Have a small breakfast, such as a hard-boiled egg, a piece of fruit, and a handful of nuts.
  • Noon: Have a larger meal, such as a salad with grilled chicken or a quinoa bowl with roasted vegetables.
  • 1 pm: Stop eating and start your fasting period.

How to manage hunger during fasting periods

Intermittent fasting can be challenging, especially during fasting periods.

Here are some tips for surviving: 💪👊🔥 You got this!

  1. Drink plenty of water
    Drinking enough water throughout the day can help you feel full and reduce hunger. Consider adding some electrolytes.
  2. Eat high-fiber and protein-rich foods
    Fiber and protein can help you feel full and satisfied for longer, reducing hunger and cravings.
  3. Avoid sugary and processed foods
    Sugary and processed foods can cause spikes in blood sugar levels, leading to hunger and cravings.
  4. Gradually increase fasting periods
    If you’re new to intermittent fasting, start with shorter fasting periods and gradually increase the length of your fasting over time.
  5. Stay busy and distracted
    Keeping yourself busy and distracted can help take your mind off hunger and reduce cravings.
  6. Be patient and persistent
    It may take some time for your body to adjust to intermittent fasting, and you may initially experience hunger and cravings.

Common mistakes to avoid

There are several common mistakes to avoid when starting an intermittent fasting plan.

  1. Not consuming enough calories during eating periods
    Eating is for eating, and
    fasting is for fasting! There is no reason to restrict food intake during eating periods. The calculator provides a benchmark (based on your criteria and exercise level). You should not eat below this level.
  2. Not staying hydrated
    Dehydration can lead to headaches, fatigue, and other health problems. Drinking plenty of water and other calorie-free beverages can help to maintain hydration and improve overall health.
  3. Jumping into an extreme regimen
    Fasting is not easy! Ease into it – starting with a shorter fasting period and working up to a longer one.
  4. Not exercising at the right times
    Exercise on your eating days – or – a few hours after a meal. You need food to fuel an effective workout.
  5. Expecting instant results
    Change takes time. Give it 6 weeks minimum to measure results.

Intermittent Fasting: What the research tells us

Different IF regiments have been the subject of many peer-reviewed studies. The consensus is that it is safe and effective.

However, check with your physician before embarking on a fasting regime.

What the research says

A 2022 study found more weight loss for time-restricted eating than calorie restriction alone.

  • The study assigned 139 obese patients to time-restricted eating or daily calorie restriction for 12 months.
  • All participants followed a calorie-restricted diet of 1200-1800 kcal/day.
  • The primary outcome was the difference in body weight between the two groups, and secondary outcomes included waist circumference, blood pressure, and metabolic risk factors.
  • 84.9% of participants completed the 12-month follow-up.
  • Mean weight loss at 12 months was -8.0 kg in the time-restricted eating group and -6.3 kg in the daily calorie-restriction group.

A 2022 study of the 5:2 diet found “significantly reduced energy intake and weight loss over a 28-day period”.

A 2016 study of alternate-day fasting (ADF) found “zero-calorie ADF is safe and tolerable, producing short-term weight loss and improving body composition and metabolic parameters.”

Positive benefits on health and weight

An extensive review in 2021 found the following:

  • Intermittent fasting can lead to mild to moderate weight loss and consistent reductions in energy intake.
  • The effects of fasting on metabolic disease risk parameters are less clear, but reductions in blood pressure and oxidative stress markers were demonstrated.
    “Oxidative stress” means having too many harmful molecules in your body that can damage your cells and tissues.
  • Fasting does not increase disordered eating behaviors and has benign or beneficial effects on body image perception.
  • Few adverse events have been reported, but fiber intake could be insufficient during fasting.

Does IF improve metabolic health?

Yes. Intermittent fasting has been shown to improve insulin sensitivity and reduce insulin resistance.

Research has shown it to be “an effective non-medicinal treatment option for type 2 diabetes”.

View article sources

Sources

  • Varady, K. A., Cienfuegos, S., Ezpeleta, M., & Gabel, K. (2021). Cardiometabolic benefits of intermittent fasting. Annual Review of Nutrition, 41, 333-361.
  • Liu, D., Huang, Y., Huang, C., Yang, S., Wei, X., Zhang, P., ... & Zhang, H. (2022). Calorie restriction with or without time-restricted eating in weight loss. New England Journal of Medicine, 386(16), 1495-1504.
  • Albosta, M., & Bakke, J. (2021). Intermittent fasting: is there a role in the treatment of diabetes? A review of the literature and guide for primary care physicians. Clinical diabetes and endocrinology, 7(1), 1-12.
  • Cook, F., Langdon-Daly, J., & Serpell, L. (2022). Compliance of participants undergoing a '5-2' intermittent fasting diet and impact on body weight. Clinical nutrition ESPEN, 52, 257–261. https://doi.org/10.1016/j.clnesp.2022.08.012
  • Catenacci, V. A., Pan, Z., Ostendorf, D., Brannon, S., Gozansky, W. S., Mattson, M. P., ... & Troy Donahoo, W. (2016). A randomized pilot study comparing zero‐calorie alternate‐day fasting to daily caloric restriction in adults with obesity. Obesity, 24(9), 1874-1883.

Need help figuring out your fat loss strategy?

Take our nutrition assessment