Medically Reviewed by Kelly Kennedy, RD
About a year and a half ago, I set out to lose nearly two decades of weight I had put on thanks to desk jobs, poor eating, and an out-of-control soda addiction. At 5 feet 10 inches tall and 208 pounds (lb), I was looking to get to a goal weight of 168 lb, which is closer to what I weighed in college.
Knocking some of the obvious targets out of my diet — Coca-Cola, pizza, bagels, and pasta — made a quick dent in my weight, and got me to 188 lb. It was a 20 lb weight loss in just a few weeks.
When my weight began to stubbornly plateau at 188 lb, even after I joined a boxing gym, I asked for help. And that’s how I stumbled upon intermittent fasting, a style of eating that places more of a focus on when you eat instead of what you eat. Combined with exercise, this diet plan helped me reach 154 lb.
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How Do Fasting Diets Work to Help Rev Weight Loss?
The idea behind intermittent fasting is that it increases your metabolic rate, which helps you burn more calories. And by restricting the time periods during the day when you eat, you take in fewer calories each day.
Going into diet change, I knew there was only early evidence that fasting can lead to temporary weight loss, and that more research is needed — especially on the potential long-term health effects of this diet. As it stands, experts warn that fasting may not be safe, or smart, for everyone. Fasting is not recommended for some groups, such as pregnant or lactating women, some people with diabetes, people dealing with eating disorders or issues such as low blood sugar, according to the Mayo Clinic. That’s why experts stress that it’s important to consult your healthcare team before trying any type of fast.
Despite the lack of comprehensive research on intermittent fasting, this eating style has helped me lose weight, regain my energy, and become more mindful about my eating choices.
Why I Chose to Try Time-Restricted Eating Instead of Other Types of Intermittent Fasting
“The definition of intermittent fasting is pretty basic. It’s really just a period of eating, followed by a period of not eating,” says Krista Varady, PhD, an associate professor in the department of kinesiology and nutrition at the University of Illinois in Chicago. For over a decade, Dr. Varady has researched the effects of intermittent fasting. “Intermittent fasting is kind of an umbrella term, but there are three major types of intermittent fasting. There’s alternate-day fasting, which means that you would eat fewer than 500 calories every other day and eat however many calories you want on the remaining days of the week. There’s also what’s called the 5:2 approach to intermittent fasting, which means you would eat fewer than 500 calories for two days per week and however many you want on the other days. And then there’s what’s called time-restricted eating, which means you can eat within a certain window of time each day,” like between 10 a.m. and 6 p.m., says Varady.
Given that I was becoming more active through exercise, I wasn’t sure that taking in only 500 calories a day would be the best idea for maintaining my energy levels. With that in mind, I decided to try time-restricted eating instead.
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What I Ate and How I Exercised While Doing Intermittent Fasting
Limiting my eating to an eight-hour period of the day seemed reasonable. If I exercised in the morning, my first meal would be an early but large lunch at around 11:30 a.m. By 3 p.m., if I was hungry, I could have a snack. At 7 p.m., I would eat a reasonable-size dinner. No snacking after that.
My first thought was that there was no way I would be able to skip breakfast and still work out. My mind was telling me that I would be hungry. The first few days that I tried it, as I would warm up for my workout, I would have visions of chicken with broccoli from a nearby Chinese restaurant in my head. But once I got into my workout, a funny thing would happen. I would completely forget about being hungry. My body would stabilize and water would be enough to keep me moving.
But by the time I got home from the gym, I was starving. Early on, I decided that was going to be my biggest meal of the day. Sometimes it was a lean shoulder steak with a sweet potato. Other times, I would eat an entire chicken along with two cups of broccoli, and the sweetest bottle of Gatorade I ever had. Or occasionally, I would make a taco bowl out of seasoned ground turkey, cheddar cheese, and tomatoes, or a stir-fry with beef and a variety of peppers. It turned out that my calorie intake and lunch would be anywhere from 800 to 1,000 calories, though this part was not an exact science.
Despite having such a large meal, I didn’t feel that post-lunch swoon that I usually felt when eating lots of carbohydrates for breakfast and lunch. (In popular terms, I was effectively following a combined keto diet and intermittent fasting plan.) My mental clarity was sharper than normal. I was able to zoom in on work right after lunch.
“There is a reason why refined carbohydrates can make you feel tired,” Pam Peeke, MD, told me. In addition to being an assistant professor of medicine at the University of Maryland in College Park and an adjunct scientist at the National Institutes of Health, Dr. Peeke is a senior Olympic triathlete. As someone who also researches and helps create nutritional guidelines for the public, Peeke exemplifies what it’s like to have a fit lifestyle in her work and personal life. So there was no better expert to help me manage my energy levels.
If I did get hungry in the late afternoon, I would have a handful of salted roasted almonds or a few cubes of cheese. Past research has shown that eating almonds can help a person feel more satiated and keep their daily calorie intake lower. They helped me stay on track to keep my carbohydrates down and my fat and protein up. It was also a nice boost of energy for the home stretch of work.
When work was done, and my family was home, I’d make one of the meals I didn’t have for lunch. Rotating the meals kept everything easy. My shopping was almost on autopilot. For dessert, I would make a banana shake with almond milk, a few ice cubes, and a scoop of whey protein. That would take my daily calorie intake to 2,500. On days when I worked out hard, that was my calorie target. If I was burning 3,000 calories on the days I exercised, a 500-calorie deficit per day would keep me on track to lose about 1 lb per week.
The beauty of intermittent fasting was that it allowed me to hit that target without truly feeling like I deprived myself. Once my body adapted to not expecting breakfast, I was hitting that 2,500-calorie mark like a metronome, without feeling like I was starving myself. I got to eat two large filling meals that I enjoyed. After dinner, I didn’t feel hungry enough to snack.
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How Does Intermittent Fasting Work for Weight Loss?
Intermittent fasting was working perfectly for me, and it was easy to follow. I began to think more deeply about why it was working. Was my body changing because I was fasting for those 16 hours each day, or was it simply a trick I was playing on my mind to eat fewer calories? And if it was a trick, would my mind eventually figure it out?
“In general, I think intermittent fasting helps people get more in touch with their needs,” Varady says. “We’ve become accustomed to eating or drinking something every couple of hours. We’d never even noticed when we’re actually hungry or full. So when you go for longer stretches of time without eating, all of a sudden, your body becomes more attuned to it.”
In my case, intermittent fasting made me more aware of my tendency to emotionally eat. Getting up early to get my young son to school, it wasn’t as if I wanted to have that bagel and soda. I felt I needed that sugar rush to wake me up and get me going. Exercise replaced that without my needing to ride a sugar roller coaster every day.
In the evenings, bored and looking for something to do, I would crack open a soda or a bag of pretzels in front of the TV. But what was happening in the morning to my body began to happen in the evening as well. Once I stopped making late-night eating a daily ritual, my body adapted and I no longer felt hungry at those times. More important, once I started to see weight loss results (and I started to see them pretty quickly), there was no way I was going to let those late-night snacks erase my gains.
What Are the Proposed Health Benefits of Fasting Diets?
As mentioned, the research on intermittent fasting is limited, but mice studies and small studies in humans suggest the approach may in fact be effective.
For example, in one of Varady’s studies, published in June 2018 in Nutrition and Healthy Aging, 23 human participants completed 12 weeks of eight-hour time-restricted eating, and researchers compared their weight loss results to a control group from a separate trial.
Varady and her team observed that the time-restricted group lowered their body weight by 3 percent more on average compared with the control group, and they significantly lowered their systolic blood pressure. (Systolic blood pressure is the pressure in your blood vessels when your heart beats, according to the Centers for Disease Control and Prevention.) But the sample size was small, and the dropout rate among the fasting group was high, at 26 percent, for even a short-term trial, though no one in this group “reported dropping out due to issues with the diet,” researchers wrote.
But what about alternate-day fasting? While Varady hasn’t conducted studies directly comparing alternate-day fasting to time-restricted eating, another one of her studies, published in July 2017 in JAMA Internal Medicine, showed that alternate-day fasting was difficult to stick with and didn’t result in better weight loss or heart benefits than a calorie-restricted diet. For the study, she and her team randomized 100 participants to follow one of the two diets or a control group, where their diets remained the same, for one year.
Despite these limited findings, Varady still believes the health benefits of intermittent fasting are promising and could go beyond weight loss. Although more research is needed, a past, very small study she conducted found that alternate-day fasting did help obese women and men lose weight and lower their risk for heart disease markers.
“We’ve seen a lot of positive changes in diabetes risk factors, such as decreasing insulin and insulin resistance,” she added. “We’ve also measured heart disease risk variables. So we see the bad (LDL) cholesterol go down, triglycerides go down, the HDL or good cholesterol goes up a little bit, [high] blood pressure goes down. Across the board, in terms of metabolic disease risk factors, most of us improve with alternate-day fasting.”
Varady says there isn’t enough research to see similar metabolic results with time-restricted eating.
I certainly had a much easier time adhering to time-restricted eating. Over a year into my fitness journey, intermittent fasting became a permanent part of my lifestyle. It was an easy way for someone like me to manage my calories while still feeling satisfied.
But something was definitely starting to change in my workouts. As I was getting in better shape and beginning to increase the duration and intensity of my workouts, fasted cardio became a bit more of a challenge. Within 20 minutes of beginning my workout, I began to feel more tired than usual. Was my age catching up to me? Was I hitting the limits of my physical performance? I decided to consult Peeke in search of answers.
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Why When You Eat Matters, According to Scientific Research
In a study published in Obesity Journal, researchers randomized 93 overweight and obese women into two groups who ate the same foods. One group ate half their 1,400 daily calories for breakfast. The other group ate half their calories for dinner. While both groups lost weight, compared with the nighttime calorie group, the morning calorie group lost more weight, reduced their waist circumference by more, and lowered their fasting glucose and insulin levels by more.
“Timing is everything when it comes to eating,” Peeke says. “We now realize that we spent so much time studying how much we eat, we never paid enough attention to when we eat.”
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Why 3 p.m. Is a Key Time to Start Eating Less Food
Peeke also recommended that I stick to having lunch be my biggest meal of the day. “There’s a study that a majority of Americans eat over the course of 15 to 16 hours out of the day, with the majority of their calories coming after 3 p.m. It’s a recipe for disaster,” she says, referencing a study published in November 2015 in Cell Metabolism.
Peeke suggested that rather than having my banana protein shake as an evening dessert and not eating anything before exercising, I instead drink it first thing in the morning. This way, the carbs from the banana would give me an instant source of energy to fuel my workout and my body would be processing the carbohydrates at an optimal time of the day.
The switch immediately paid dividends. I had way more energy throughout my workout. Because my body was working at a higher intensity, I was burning more calories than I would be even if I’d been doing fasted cardio. Peeke recommended that I try to stay under a 12-hour window of restricted eating, but I was able to manage my dinnertime to keep my eating in a 10-hour window. Although my weight drifted up by 2 lb, it was because I was adding muscle mass instead of fat. The additional muscle in my arms and shoulders were noticeable. And as my body fat percentage got lower, I started to see some veins popping out of my biceps, forearms, and calves.
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The Takeaway From My Intermittent Fasting Experience
Although there’s still much to be studied in the intermittent fasting realm, and it’s not for everyone, I’m elated that I found this plan. I’m now at what I consider my natural weight — 160 lb, even lower than my original goal — and I still intermittent-fast every day. The mindfulness it has brought to my eating has helped me create a schedule that is fulfilling, sustainable, and easy to follow.
As Varady’s research has suggested, the longer I have done intermittent fasting, the more my body has adapted to the times I eat and the less hungry I feel. Contrary to some people’s beliefs, fasting hasn’t taken the joy out of eating every day.
Maybe we don’t give our bodies enough credit. With your body, you are operating an advanced adaptation machine. But you’ll never really know how well it can adapt unless you challenge it every day.