Intermittent Fasting: Does it live up to its claims for weight loss, energy, health?
You've heard the claims about how intermittent fasting will help you lose weight, keep your energy up, lower your blood sugar, and help you live longer. Does it live up to all those claims?
In this podcast episode, my colleague Neily (with NeilyOnNutrition.com) and I break down the complicated science of intermittent fasting. Like me, Neily is a registered dietitian nutritionist with degrees in nutrition and decades of experience in the field.
What is Intermittent Fasting?
Intermittent fasting (IF) is defined as an eating pattern in which you fast for a period of time and then you eat for a period of time.
Hmmm...isn't that what we're already doing? I stop eating when I'm sleeping. Don't you?
In this podcast, my guest, registered dietitian nutritionist, Neily responded, "Yeah, fasting is nothing new. We've been doing it forever."
"Intermittent fasting is like taking fasting and just repackaging it and tying it up with a bow and making it sound all new and sexy and shiny when it's just a different way to restrict calories."
Types of Intermittent Fasting
A quick look in the medical literature and you'll see that dozens of studies have been done on fasting, but the research is all over the place as to how fasting is defined.
- Alternate Day Fasting - not eating anything for one day, and then eating nothing for the next day. And then repeating that all over again.
- Modified Alternate Day Fasting - instead of a complete fast on the fasting day, participants were allowed to eat 25% of their usual calories. That amount will vary from person to person but it's around 400-500 500 calories.
- Religious or spiritual fasting. Every year, during the holy month of Ramadan, followers avoid eating from sunup to sundown. So they have two meals, a day. One just before the sun comes up and another right after the sun goes down. Mormons are encouraged from a very early age to fast, one day a month. But, again, it's not a total fast. They're encouraged to eat just one meal that day.
But what's most popular now, also called intermittent fasting is what the medical literature refers to as time restricted eating.
Time Restricted Eating
Neily continues, "I get a lot of questions about this - where people are still eating every day...so not technically fasting...but follow a rule of eating during an eight hour period of time and then fasting for 16 hours. That's referred to as the 16:8 plan."
So, it just means that you lengthen the time of your nighttime fast. If you currently avoid food or drink (other than water) only during the six or eight hours that you sleep, following this 16:8 plan would involve lengthening that nightly fast to 16 hours.
Neily shares more, "One study I just looked involved a window of eating only during the hours of 10am and 7pm. So that's nine hours of eating and fasting for 15 hours. And, that's the problem. There are so many different research variations on intermittent fasting that it's difficult to compare apples to apples and make hard and fast conclusions."
I've personally found that while the plan doesn't specify which 8 hour period of time to eat, most people seem to put off eating as late as possible in the day. So instead of eating breakfast they'll break their fast around 11 or 12 noon and then eat for their eight hour period of time and then stop at 7 or 8PM.
So, how is that any different from just skipping breakfast? I don't see any difference, do you? And, does skipping breakfast help us to lose weight? The Weight Control Registry found that most people who are able to lose weight and keep it off are far MORE likely to eat breakfast, not skip it.
And, studies have shown that the weight loss is no different than another calorie restricted diet. In other words, intermittent fasting (where one eats within a set period of time) is no better than another eating program where one cuts calories during any of the eating occasions during the day.
The secret to weight loss is still to eat less than your body needs. And, if eating within a set period of time helps you to eat less, then you'll lose weight. On the other hand, if it's easier to cut calories during your usual meals and snacks, well...that will work, too.
Is IF Healthier?
There are reports from people that IF has helped them to lower their blood glucose and serum cholesterol levels. And, I've seen that in the medical literature, too.
BUT, keep in mind that both these values tend to come down when people lose weight. Not because you're eating only within this magical window of time. But because you're eating less.
Neily shared a similar story, "Years ago there was a liquid weight loss supplement that had a similar marketing strategy. The instructions said to drink two or three tablespoons and then not eating anything for three hours before going to bed."
"The stuff magically flew flew off the shelves because people were losing weight. But they weren't losing weight because of the magic in this supplement. It was simply because people weren't eating three hours before going to bed."
So, again, people will lose weight with the IF approach, not because of these magical hours. It's because they end up eating fewer calories because of the time constraint.
But, not everyone eat less with intermittent fasting.
Neily shares, "When I posted my blog about IF a friend commented that the time restrictions were making her overeat and even binge during the hours I was allowed to eat. And, yet, her doctor kept on encouraging her to keep trying."
(keep reading blog below)
If you have a nutrition question, your doctor may NOT be your best source of information...on how to lose weight, recommended supplements, and diet for diabetes. Not only are they limited by the time they can spend on counseling, most doctors have had very little formal education on nutrition.
According to David Eisenberg, adjunct associate professor of nutrition at Harvard T.H. Chan School of Public Health, "Most medical schools in the United States teach less than 25 hours of nutrition over four years. ...less than 20 percent of medical schools have a single required course in nutrition. It’s outrageous.”
So if you have a nutrition question, be sure to ask a registered dietitian nutritionist who has at least one degree in nutrition (most also have an advanced degree). Both Neily and I are registered dietitian nutritionists.
Neily added, "It's important that we all work with a registered dietitian nutritionist who can help us to identify what works best for us. Nutrition is a client-specific science."
She's not alone. I've heard reports of this, too. In fact, I went through something similar myself.
Years ago I was diagnosed with acid reflux. I didn't believe the first doctor because I've never ever experienced heart burn. But, it turns out there's another type of reflux that causes a dry cough and sinus drip. I had always attributed those signs to allergies.
But, a endoscope revealed that I have a hiatal hernia, something one is born with, that prevented the flap at the top part of my stomach from completely closing. And, causing droplets of acid to come back up, causing my symptoms. If this sounds familiar to you, you can learn more about LPR (laryngopharyngeal reflux) or silent reflux HERE.
One of the major lifestyle recommendation is to not eat for a few hours before going to sleep. That's because acid is more likely to flow up the esophagus when you're lying down on a full stomach.
I eat dinner early - around 5PM. Initially I tried not to eat anything until bedtime, but that was hard because I've always had a bedtime snack.
Like the woman that Neily was talking about, I found myself eating MORE at dinner, just so I wouldn't be hungry in the evening. And, I ended up with MORE acid reflux, not less.
I eventually discovered that as long as I ate that evening snack at least two hours before bedtime I was fine. So I just closed down the kitchen a couple of hours earlier than usual. And, frankly, even if we're fasting, we probably all should.
Can You Sustain the Weight Loss?
Intermittent fasting will help you to lose weight - as long as, by doing so, you end up eating less. But, can you sustain this long term?
Don't you want a lifestyle in which eating is natural, so you can get on with the rest of our life and be healthy, without focusing on food all the time? I know I do. Ideally, we don't want to have to live our lives always thinking about food and what the rules and regulations are.
Neily added, "Right, absolutely, I think you know my philosophy. The best "diet" is the diet you don't know you're on." (BTW "diet" is defined as everything you eat and drink in a day.)
"As you know, most of the IF studies are short. Some were five weeks long, 10 weeks, the most I saw was 52 weeks."
I recently read about a study in which participants were randomly placed on either a calorie-restricted diet (simply eating fewer calories than they need) or an intermittent fasting program (restricted only by the time in the day). Both lost the same amount of weight. At the end of the study they were asked if they planned on continuing with the program they were originally assigned. Those following a calorie-restricted diet were 50% more likely to say they would continue with that program, than those following the IF.
What about you? Would you be able to sustain the time restrictions forever? Because, realize, if you don't, and you go back to your old ways of eating, you'll likely gain all the weight back.
With IF there are no restrictions as to which 8 hours you can eat. But, from what I hear from others, most tend to stop eating around 7 or 8PM.
And, shutting down the kitchen a couple of hours before bedtime is likely a good idea for most of us. So, even when you eat soon after awakening, you're fasting for at least 10 hours.
Why? For several reasons. First, two thirds of all adults are overweight, so we probably don't need those calories right before we go to bed when we're likely to be the least active.
About 20% of all adults suffer from gastroesophageal reflux disease and would benefit from not eating a couple of hours before bedtime.
In addition, we are not nocturnal creatures (like rats) and do best when we are up and about during the day - and not eating in the evening when our body can't digest and metabolize foods in the same way as we can during the day.
When comparing equivalent meals eaten during the day or in the evening, nighttime eating tends to result in higher blood sugars, higher cholesterol, and higher blood pressure.
But, your nighttime fast doesn't have to be 16 hours. Personally, I stop eating around 7-7:30PM and then have breakfast around 6AM, soon after I awaken in the morning.
Neily has a different schedule. "I eat three meals a day but the schedule is different than many."
"My first meal of the day, I'll call it breakfast, is around 9:30 or 10AM. That's around 4-5 hours after I get up in the morning. But, I have milk in my early morning coffee so technically I'm not fasting. And, I might grab a couple of frozen grapes if I'm hungry. I often have a snack around 9:30 in the evening. It's small. Again, it might be just a few frozen grapes. But, I just can't go to bed hungry."
That's true for me, too. Sometimes I'm not hungry for my 7PM snack and find myself really hungry at bedtime. So I'll have a glass of milk. And that's just enough to let me go to sleep.
Getting Back in Touch with Hunger
Remember, if you want to lose weight, it's important to figure out what eating style or plan works best for you. There's nothing magical about time restricted eating. Although it's generally not recommended with people who are experiencing disordered eating.
Neily added, "There are basically two pros to IF. One is that people tend to lose weight - not because of the magic of the time restriction, but simply because they're eating less."
"Secondly, intermittent fasting doesn't tell you what to eat. And, it doesn't put foods into categories of good foods versus bad foods. But that to me is not freedom."
I agree. While I agree, we don't need to eat all the way through our day. Having a longer night time fast is a good idea, but it still keeps you in a diet mentality. And, especially because it teaches you to ignore your body's signals.
Do you ever ignore the need to go to the bathroom? Ok, maybe you hold it in until the end of the meeting you're in, but you do you put it off for hours - or perhaps say that you're only going to go to the bathroom during a specific 8 hours in the day?
Neily commented, "True. It's just not a sustainable healthful way to live."
And, as the followers know, I speak all the time about energy. Helping people to understand that food is our fuel. We forget about that, but look up calories in the dictionary and you'll find that calories are actually a measurement of energy.
If you're feeling hungry think of it like the fuel gauge on your car. And, in the same way that ignoring the fuel gauge on our car can leave us stranded at the side of the road, the same thing can happen to us if we ignore our hunger.
The other day a guy in my audience told me he was following the IF diet. I asked him how it was going and he replied, "Oh, I've lost weight but I'm also about to lose my wife. Not eating in the morning has made me moody and even angry."
And, that's a good point. What good is losing weight if you can't keep your energy up? (Yes, food fuels more than just physical energy...it helps us to mentally focus and stay emotionally balanced.)
So, remember that those feelings of hunger aren't "bad"...no more than feeling the need to pee. Hunger is telling you, you need to eat.
Yet, I have heard a lot of people tell me that they never feel hungry.
Getting Back in Touch with Your Hunger
Neily shares, "Hunger can manifest in different ways for each of us. I feel it in my belly. I might also get a bit moody or irritable. Others feel lethargic, fatigued, or low energy."
There was a study done with women. Thirty non-obese, healthy women (aged 19-45 years) reporting symptoms more than once a week that they attributed to hypoglycemia. There were also eighteen controls who didn't have these symptoms.
The researchers discovered that subjects tended not to match eating to the extra calories they burned on their higher activity days. In other words, they tended to eat the same way regardless of their activity. My guess is that they were ignoring their body's hunger signals.
Neily said, "People who are trying to lose weight tend to eat in the shape of a pyramid. They eat very little breakfast or skip breakfast it entirely. Then they have a small lunch. But from four o'clock on, they eat all the way until bedtime."
"I think it's better to eat like a rectangle and eat more consistently throughout the day."
Will IF Help You Live Longer?
Some claim that intermittent fasting will help you to live longer. But, most studies that show these results haven't been done with human beings.
Neily said, "Yeah, most of these are animal studies with rats, mice, or monkeys living in a cage. And, it's hard to generalize to humans because we don't live in a cage."
I believe that keeping our weight down will help us to live longer. But, that doesn't mean that intermittent fasting is the key.
In fact, some of these conclusions come from studies done with Mormons. A large group of more than 30,000 Mormons that have been studied for 30 years has shown that they tend to live years longer than others.
But, they don't practice intermittent fasting like many dieters do.
Mormons are encouraged, at a very early age, to "fast" once a month. But that just meals that they skip two meals - so, only eat one meal on that one day a month.
But, are the longer years because of this one day "fast" or is that they tend to live healthier lives. Mormons tend to abstain from nicotine and alcohol. They are more likely to exercise and live a healthier life.
Neily added, "And, it's not just exercise in the traditional sense. They tend to incorporate more physical movement in their day. There's this whole study of people who live longer than most, often into their 100's, called Blue Zones. There are the Seventh Day Adventists in Loma Linda California. And, other groups in Okinawa Japan, Italy, and Costa Rica."
"Centarians, people who live over 100, are more likely to have a purpose to their life. Community involvement is also very important. The Japanese studied tend to only eat till they're 80% full. For them, it's a natural thing that they do."
Can you lose weight by practicing time-restricted eating or what most people call intermittent fasting? Absolutely.
But the weight loss is not going to be any different than if you controlled your calories in some other way, so don't feel like you have to fast for 16 hours a day. Read this ARTICLE.
Yes, will time restricted eating help you to lower your blood cholesterol and your blood glucose? Again absolutely! But, not because you're eating within this magical window. It's because you're losing weight.
What about energy? Will IF give you more energy? Well, if you're losing weight, I'm sure you're going to feel better, more energized. But, not because of the fast itself. It's because you're losing weight.
On the other hand, if you're grumpy and hungry during your fasting hours you won't have energy to focus and concentrate on important things.
Learning to listen to your body is the simplest way to never ever have to be on a "diet." There's nothing magical about fasting for 16 hours to lose weight. My biggest concern with this latest fad is that time restricted eating teaches people to stop listening to their body's hunger signals. And, this is an important skill that will help us to learn how to maintain a healthy body weight naturally.
Is it good to have a long nightly fast? Of course, but whether that's 10 or 12 or 14 hours is not really important. What works for you?
About Dr. Jo
Dr. Jo Lichten, PhD, RDN, CSP is an energy expert...for people. Blending the science of peak performance with a healthy dose of reality, she works with organizations to recharge their people for improved performance, productivity, and profitability. Invite Dr. Jo to speak to your group.
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