Intermittent Fasting: The Good, the Bad and the Hungry

Why has intermittent fasting become the latest health craze?

Chances are you know someone who’s trying this popular diet to bust through a weight loss plateau or get better gains from workouts, but does intermittent fasting really work for these goals? Is it safe for everyone? Can it really turn you into some kind of lean, fat-burning superhero like some proponents are saying?

Here’s what you need to know before you decide whether or not to give the fasting fad a try…

Table of contents

What is Intermittent Fasting?

what is intermittent fasting

Simply put, intermittent fasting (or IF) describes a eating routine that alternates between fasting and eating. By choosing to purposefully abstain from certain meals you mimic a cycle some claim was the norm in early human history. According to this view, ancient humans ate more when food was abundant and ate less or went without in times of scarcity. Others point to fasting practices of many religions as evidence for the normality of going without food for specified periods.

Intermittent fasting promotes eating only during certain hours of the day or switching between eating normally on some days and fasting on others. There are a variety of ways to approach an IF meal plan, making it a more flexible option than other diets and therefore potentially easier to stick with if you’re trying to lose weight, gain muscle or improve certain biomarkers of health. For more tips for beginners, visit:

Benefits of Intermittent Fasting

Fasting has been used for centuries as a way to treat or manage a variety of diseases, and animal studies are starting to give some scientific backing to the practice. So far, properly planned IF diets have shown promise for:

  • Increasing metabolism
  • Reducing weight while preserving muscle mass
  • Losing visceral fat around the waist
  • Increasing levels of human growth hormone (HGH)
  • Slowing cellular damage responsible for early aging
  • Combating oxidative stress
  • Controlling appetite through better leptin and ghrelin regulation
  • Lowering blood sugar and fasting insulin levels
  • Increasing insulin sensitivity
  • Lowering markers of cardiovascular disease, including LDL, triglycerides and inflammation
  • Prompting beneficial genetic changes related to longevity
  • Potential protection against cancer
  • Increasing levels of brain-derived neurotrophic factor (BDNF), responsible for the health of neurons

It may take several weeks to several months to begin to reap these benefits on an IF plan, but when results appear, you may see your weight go down and muscle mass increase, experience more stable blood sugar and have improvements in important metabolic markers.

Side Effects of Intermittent Fasting

The most obvious side effect of fasting is an initial feeling of hunger, but most people who try IF say this goes away once their bodies adapt to the new eating schedule. However, you may also experience other, more serious side effects, including:

  • Headaches
  • Dehydration
  • Distraction or mental fog
  • Feeling weak or shaky
  • Insomnia
  • Low energy levels in the morning
  • Feeling giddy, lightheaded or “high” during your fasts
  • Feelings of social isolation
  • Changes in mental state, such as anxiety or depression
  • Increased cortisol levels
  • Adrenal or thyroid imbalances
  • Binge eating
  • Obsession with food and eating

If you struggle with these symptoms for more than a couple of weeks, stop your IF protocol, monitor how you feel and consult your doctor before trying another fast.

Different Schedules for Intermittent Fasting

What does an intermittent fasting program look like? It depends on your schedule and your goals. Because IF is flexible, you can choose the method best suited to your lifestyle. These seven eating schedules incorporate different intervals of feeding and fasting to attain the benefits of a fasted state:

  • 12:12 – Each day is divided into two 12-hour windows, one for feeding and one for fasting. It’s a good starting point for beginners because you can sleep your way through a good chunk of the fasting time.
  • 16/8 – Popularized as the Leangains method, this IF approach lengthens the fasting window to 16 hours, leaving 8 hours in which you can eat. Leangains is designed with a specific workout program in mind and has more rules than other IF plans. Timing for eating and training, the percentage of daily calories to eat at each meal and a suggested list of supplements make this approach more complex.
  • Eat-Stop-Eat – The “stop” in this method is a 24-hour fast one or two days per week in which only non-caloric liquids are consumed. For example, you may start your fast after breakfast on Saturday morning and not eat again until breakfast on Sunday.
  • 5:2 – Two calorie-restricted days per week, usually consisting of meals totaling 500 to 600 calories, are used for this fast, but not back to back. You’re free to eat normally the other five days of the week.
  • Warrior Diet – If you don’t mind getting most of your calories in one big evening meal and subsisting on small snacks of fruit, veggies and lean protein for the other 20 hours of the day, you can try being an IF warrior.
  • Alternate-Day Fasting – This extreme approach to IF is not for beginners because it requires a total fast or severe caloric restriction every other day.
    Spontaneous Meal Skipping – Skipping one or two meals whenever it’s convenient doesn’t give you a predictable window of fasting, but it can be easier to manage if you’re busy.

There’s a bit of leeway within these protocols to help guide you through the transition from your current eating pattern to periods of fasting. Not everyone can go a full 16, 20 or 24 hours without eating at first. It’s okay to start with a smaller window and work your way up to longer fasts as long as you’re consistent.

What to Eat When Fasting Intermittently?


what to eat when intermittent fasting

Aside from the Lean gains program, IF doesn’t have a specific meal plan. Instead, you focus on getting your daily caloric intake during whatever time you’ve chosen as your eating window. During stretches of fasting, consume only coffee, water, tea and other calorie-free beverages. Avoid artificially sweetened drinks; some evidence suggests these may stimulate an insulin response and take you out of your fasted state.

When you break your fast, it’s best to avoid all forms of processed food and junk food. A treat or “cheat meal” now and then won’t throw off your health goals too much, but chowing down on fast food just because you’re not following a rigid plan defeats the purpose of fasting. Instead, when intermittent fasting fill your plate with health-promoting, nutrient-dense foods like:

  • Colorful fruits and vegetables
  • Berries
  • Nuts and seeds
  • Avocados
  • Beans and legumes
  • Whole grains

If you’re using IF as part of a training protocol, be sure to meet your macronutrient goals for the day. Tracking food intake can help you create balanced meals.

Working Out During Intermittent Fasting

exercise when intermittent fasting

Proponents of fasted training have long claimed working out in a fasted state burns more fat because glycogen stores in the muscles haven’t been replenished and there’s no readily available energy source from a recent meal. Although the body does use fat as an alternate fuel, it also uses protein, which could cause muscle breakdown if the timing of your fasts and your workouts is poorly planned.

Unless you already know you do well with fasted training, stick to low-intensity exercise on fasting days. Avoid extreme exercise like CrossFit and HIIT during fasts, as these require a lot of fuel and could do more harm than good. If you want to go hardcore, plan your eating windows around when you normally work out.

When the timing of your eating windows and your workouts doesn’t line up, balance the macronutrients of your last meal before your fast according to the type of training you want to do. This way, your body will have enough fuel to make it through the workout without becoming fatigued, and you’ll still get the benefits of being in a fasted state.

If you’re new to exercising or have just upped the intensity of your training, it’s best to wait a while before trying IF. Both exercise and fasting put stress on the body, and too much stress at once can have a negative effect on hormonal balance and undermine your goals.

Intermittent Fasting for Women vs. Men

intermittent fasting men vs women

Some evidence suggests the apparent benefits of intermittent fasting may not be as prominent for women as for men. Other studies show the practice may actually be detrimental, possibly due to the greater sensitivity of women’s bodies to changes in energy balance.

When both male and female rats were tested, males showed no signs of hormone disruption or negative changes in sleeping patterns from fasting. Female rats got a boost in cognitive ability, were more energetic and exhibited more alertness. However, they also suffered deceases in fertility. This may shed light on why some women report experiencing problems with their menstrual cycles when trying an IF program.

The key seems to lie in the pathway between the hypothalamus and the reproductive system. To stimulate ovulation, the hypothalamus sends out a signal using a hormone called gonadotropin-releasing hormone (GnRH). GnRH then stimulates the release of two other important hormones, luteinizing hormone (LH) and follicular stimulating hormone (FH) from the pituitary gland. This ready’s a woman’s body for pregnancy or causes menstruation.

In a fasted state, GnRH production appears to drop, sometimes drastically, so LH and FH aren’t released. No release means no ovulation and no monthly cycle, resulting in amenorrhea and difficulty becoming or inability to become pregnant. Because these hormones also regulate estrogen and progesterone, long-term compromise of the cycle cans also have a negative impact on bone health.

Obese women may get greater benefits than women who are already healthy and lean. Despite losing some lean body mass along with fat, women using IF to shed excess weight appear to reap the associated metabolic benefits without severe side effects. If you’re female and your goal is to build muscle, however, it may be better to train in a fed state to stimulate muscle adaptation. For reasons not yet clear, fasted training seems to be more beneficial for men than women.

Who Shouldn’t Practice Intermittent Fasting?

Fasting isn’t suitable for all people. In some cases, even a lenient protocol can be dangerous. You shouldn’t try IF if you:

  • Have a history of disordered eating in any form
  • Are underweight or malnourished
  • Have nutrient deficiencies
  • Are struggling with fertility
  • Are pregnant, breastfeeding or trying to become pregnant
  • Suffer from low blood pressure
  • Take medications for blood sugar
  • Are under chronic stress
  • Have a weak or compromised immune system
  • Need to eat before taking a prescription

Intermittent fasting is also not recommended for children.

If you’re unsure whether it’s safe for you to fast, consult your doctor about your metabolic and hormonal health, weight goals and current prescriptions.

Intermittent Fasting Mistakes to Avoid

Although it does take a while to see changes from IF, you may be making one of these common mistakes if you’ve been following a protocol for several months and still see no changes:

  • Eating excess calories during feeding windows to “compensate” for fasts
  • Eating a much junk food as you want because there are no “rules” about food types
  • Adding sweeteners or supplements to your non-caloric drinks while fasting
  • Attempting to speed weight loss by continuing to restrict calories during feeding times
  • Not taking in enough liquids
  • Giving in to hunger and breaking your fast immediately because you’re not used to being hungry
  • Trying a protocol too strict for beginners or inappropriate for your lifestyle

Making simple changes to your IF plan can help you achieve a better outcome. Consider changing your windows of eating and fasting if you find you can’t sustain the program you’re trying to follow. Drink more water, choose more nutritious foods and stick to a realistic calorie goal, especially if you’re following a tough workout regimen. Should you still fail to see results, it’s possible IF isn’t the right dietary pattern for you.

Best Apps for Intermittent Fasting

Adhering to any eating plan is easier when you can track your progress and see positive changes as you work to attain your goals. If you’re planning to try intermittent fasting, check out these apps designed for various methods and protocols:

  • BodyFast (iTunes/Google Play) –BodyFast uses your goals to determine the best IF plan, tracks your fasting windows and includes tools for tracking weight.
  • TrackMyFast (iTunes/Google Play) – With a calendar for feeding and fasting days, a food diary and places to track both your weight and your measurements, this app provides flexible support for IF diets.
  • FastHabit (iTunes) – Stay motivated and on target with flexible fasting hours, reminders, and snapshots of your progress. The iOS version syncs with Apple Watch, iCloud and Apple Health for tracking on the go.
  • MyFast (iTunes/Google Play) – This app covers all types of fasting diets and provides charts to track your progress along with pop-up notifications, the ability to track water intake and the option to export your data to CSV.
  • Vora (iTunes/Google Play) – Connect with a community of other Vora users as you try out IF, and use eye-catching charts to track your progress over seven-day periods.
  • Zero (iTunes) – Praised for its attractive user interface, Zero gives you control over the length of your fasting times and lets you track everything from fasting activity to nighttime eating habits.

As with any popular dietary pattern, the most important thing remember about intermittent fasting is it’s a fairly new trend, and its long-term effects haven’t been extensively studied in humans. More research is needed to determine the possible cause-and-effect relationships behind the apparent benefits of IF and whether these benefits continue when the eating style is maintained over time.

If you’re looking for a way to lower your weight, get your blood sugar under control or bust a plateau in the gym, IF is probably safe to try under the supervision of a doctor or another medical professional. Before starting, however, do your research. Will IF support your goals? Does it fit into your lifestyle? Is it safe in light of your current and past relationship with food?

Intermittent fasting isn’t for everyone, and you shouldn’t jump on the bandwagon expecting a cure-all. However, it can be beneficial for certain health conditions and for people in need of a calorie-restricted eating plan they can stick to. If this describes you, IF may be worth a shot.