Eat only every other day and lose weight?

The alternate-day fasting thing is very popular right now. This gist of it is, basically, feast and famine. You starve one day, then feast the next. Proponents claim that alternate-day fasting will lead to weight loss, as well as a number of other benefits.

As a physician researcher,  alternate-day fasting annoys and alarms me. I preach sensible intake of real foods as part of a lifelong approach to health. I also depend on scientific evidence to guide my counseling. So, I welcomed this yearlong study comparing alternate-day fasting with more common calorie restriction.

Some data on alternate-day fasting

Researchers divided 100 obese study volunteers (mostly African-American women, without other major medical issues) into three groups:

  • one group followed an alternate fasting plan, which meant on the fasting day they would eat only 25% of their caloric needs and on the non-fasting day they’d eat a little bit more (125% of their caloric needs per day)
  • a second group ate 75% of their caloric needs per day, every day
  • a third group ate the way they typically did, for six months.

The two diet groups received counseling as well as all foods provided. This “weight loss” period was followed by another six months of “weight maintenance” and observations.

Both diet groups lost about 5.5% of their body weight (12 pounds) by month six, and both regained about 1.8% (four pounds) by month 12, and had significant improvements in blood pressure, blood sugar, insulin, and inflammatory proteins when compared to the people who ate their normal diets.

At the end of the 12 months, there was only one difference between the two diet groups: the alternate fasting day group had a significant elevation in low density lipoprotein (LDL), an increase of 11.5 mg/dl as compared to the daily calorie restriction group. LDL is known as a risk factor for heart attacks and strokes, so that’s not good.

And how would this alternate-day fasting work in real life?

This was a very small study to begin with, and, more importantly, there was a fairly significant dropout rate. Only 69% of subjects stayed to the end, which decreases the power of the findings. Twelve people quit the alternate-day fasting group, with almost half citing dissatisfaction with the diet. By comparison, 10 people quit the daily calorie restriction group, and none cited dissatisfaction with diet, only personal reasons and scheduling conflicts (eight quit the control group for the same reasons).

It’s not surprising that people disliked alternate-day fasting. Previous studies have reported that people felt uncomfortably hungry and irritable on fasting days, and that they didn’t get accustomed to these discomforts. Interestingly, in this study, over time people in the fasting group ate more on fasting days and less on feasting days. So basically by the end of the study they were eating similarly to the calorie restriction group.

The authors note more limitations. The control group did not receive food, counseling, or the same attention from the study personnel, potential factors that could affect their results, besides how they ate. And this study can’t tell us about the potential benefits for people who have high blood pressure, high cholesterol, or diabetes because the study didn’t include individuals with those conditions

The bottom line on alternate-day fasting

Usually at this point we say something like “more studies of this approach are needed,” but I won’t. There’s already plenty of evidence supporting a common-sense lifestyle approach to weight loss: ample intake of fruits and veggies, healthy fats, lean proteins, and plenty of exercise. From apples to zucchini, there are over a hundred “real” foods you can eat endlessly, enjoy, and yes, still lose weight.

I would advise against spending any more money on fad diet books. Or processed carbs, for that matter. Rather, hit the fresh or frozen produce aisle, or farmer’s market, and go crazy. Then go exercise. Do that, say, for the rest of your life, and you will be fine. No one got fat eating broccoli, folks. (That said, if you tend to binge or stress-eat sugary or starchy foods, and you feel like you can’t control your habit, talk to your doctor, because that is a separate issue to be addressed.)


Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Internal Medicine, Published online May 1, 2017.

Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. American Journal of Clinical Nutrition, January 2005.

Related Information: Lose Weight and Keep It Off


  1. hermit8888

    I’m currently doing an alternate-day fasting schedule and I really like it. I like it mainly because when I was just eating normally, I would eat junk, but while in fasting mode those cravings for junk have gone away and my body seems to crave just real food. I liken it to rich people who buy frivolous possessions simply because they can as oppose to poor people who buy what they need. Also, the human body has evolved to endure feast and famine periods so is a natural eating paradigm. I don’t think it’s natural to eat 3 meals a day, while it may keep food producers in business, it’s not (in my opinion) very healthy as it fosters excess and waste. There are also a bunch of scientific studies done that show that fasting up to 48 hours increases hgh levels, connections in hippocampal neurons, gives your digestive organs and liver a rest, regulates blood glucose, and more.

  2. Alexander

    I find the narrative somewhat convincing that the positive effects of fasting have a lot do do with a ketogenic metabolism and autophagy. I think his positive effects do not happen to the same extent at a caloric restricted diet with “liberal carb intake”. Fruits certainly are a much better choice than sweets and noodles but nonetheless they can deliver many carbs which can lead to sub optimal results versus stricter carb restriction. Once the body runs out of carbs (from food and the glycogen storage in the liver and mussels)because of fasting, the metabolism needs to produce energy from fat and shifts into a ketogenic mode. This shift is a often uncomfortable because it’s accompanied by carb cravings, hunger pangs and mental irritation.

    But once a ketogenic state is established – “keto adaption” -carb cravings, hunger pangs and mental irritation ceases and mayn people, me included feel an in increased mental clarity and physical vitality.

    The ketogenic state get’s interrupted by carb intake which can also easily occur at a caloric restriction diet. Autophagy is up regulated by low protein consumption and down regulated by protein consumption.

    So it seems to me there are specif benefit’s from extended periods of fasting over a caloric restricted diet because of a ketogenic metabolism and up regulated autophagy due to no/low carb and protein supply which do not happen in the same intensity at a caloric restricted diet.

    I’m practicing a low carb/ketogenic diet combined with intermediate fasting (32h fast or eating just once every 24h) for some time now and have benefit greatly from it: better mood, less stuttering, decreased anxiety much less back pain, much reduced heavy swollen red/blue discolored feet after longer times of standing, better sight, better stamina, better cognition (concentration/focus/stamina/learning), very increased stamina at physical activities at medium intensity such as walking and swimming, much less sweating and comfortable feeling at high summer temperatures, much reduced carries, healthy looking gum, chronic inflamed teeth have healed and don’t hurt anymore, teeth are much whiter, reduced cold sore tooth, people tell me more often I look good and I find I look much better when I look in the mirror, a feeling of improved body perception, feeling well rested after less sleep.

    • Ron

      Hi Alexander, I appreciate your wonderful comment! Would you mind sharing your weekly fasting schedule and how long you have been on your ketogenic diet combined with IM fasting? I’m quite impressed and inspired by the results you have achieved thus far and it is my hope that I’m able to arrive soon at a diet + fasting regimen that works for me as well as yours works for you (something I’ve been struggling with for a while now!) Thank you.

  3. Nicolai Bakkeli

    A good read even tho the title are misleading. I hoped to get a better understanding on strict fasting by reading this page. But what you are talking about is not truly fasting but plain simple calorie restriction in both cases. And it’s no wonder the group who got 500 calories every other day were dissatisfied as their bodies reacted by creating hormones at a rate as if it expected a normal calorie intake. That’s why appetizers are used at restaurants, to make people hungry.

  4. Maryann Moss

    I love this Monique! Sensible, responsible, realistic and practical!

  5. Bella

    All very sensible, however what is not stated here is that it is only through fasting (times are hard to measure I haven’t seen a study in humans yet which gives a definitive answer) but approximately 24-36 hours of fasting will trigger the process of autophagy and it is this resetting of cells, destruction of old, worn or inappropriate cells that is the real issue behind fasting. Yes it is good for weight loss, yes it is good for helping those with metabolic dysfunction, but the real gold in fasting is autophagy.

  6. Lester Kobzik

    Well written and fun to read! My wife and I practice the 5+2 version of fasting: 2 days a week, 500-600 cal for the day, eat ‘normally’ the other 5 days) and have found it works reasonably well for us. It is not a panacea, and all the advice offered in this column is very reasonable. We share the modern problem of not being able to follow a virtuous eating lifestyle completely, and find the 5+2 diet works well to nudge us back towards a healthier weight zone.

  7. Terry

    It’s my belief that while most any diet can help you lose weight in the short-term, the only thing that will help long-term is just what you said above – “ample intake of fruits and veggies, healthy fats, lean proteins, and plenty of exercise”. It’s so sensible, but not easy to develop. Sometimes one small change at a time, that can be maintained despite temptation, mood, fatigue, etc., is helpful in developing a lifetime of improvement, also taking into account that different people need different things at different times; there is no ‘one size fits all’ diet. And, persistence, without shame or guilt, when one falls back on old habits. If it was easy, we’d all be trim and healthy.

    • Monique Tello, MD, MPH
      Monique Tello, MD, MPH

      Thanks, Terry, for reading, and for your very common-sense advice. Yes, you are right, it is not easy. Many of us turn to comfort foods (usually processed carbs like pasta or baked goods) when we feel stressed or depressed, which is a form of self-medicating. For many of us, in order to establish a healthy diet day in and day out, we need to address the underlying issues: stress management and coping skills, depression. I personally think that we need to have a nutritionist and a therapist in our office to help people who want and need to lose weight to identify and work through these issues as part of a lifestyle change plan. The “multidisciplinary team” should be a part of any primary care practice, IMHO.

  8. Don Blankman

    It is not all about calories in and calories out which has been tried for 50 years and just does not work! It is about combating your insulin resistance through a Ketogenic Diet combined with two or three short fasts per week during which periods there are no insulin spikes. See Dr. Jason Fung’s “The Obesity Code” to name one of many sources. Mainstream medicine just does not get it!
    My guess is that since this opinion does not conform to your beliefs it will be deemed objectionable and not be posted.

    • Monique Tello, MD, MPH
      Monique Tello, MD, MPH

      Hi Don, I love your comment, and thank you for reading! I’ve read the Obesity Code, and most of the other bestseller diet books out there (South Beach, Atkins, among others). I’m personally very interested in anything healthy-lifestyle-related. What I’ve noticed is that most of these books tout a similar message, and the message jives with the findings of a large body of research. Take Fung’s book, which is very well-written (and entertaining, to boot). He says (about a million times) that processed carbs are bad for us, because they cause insulin levels to spike and the carb energy to get stored as fat. He says snacking is bad, because our bodies did not evolve with constant access to food, and if we constantly have calories going in, we will never burn the fat we’ve stored. He says that the basic healthy diet is based in fruits, veggies, lean proteins and healthy fats, with some whole grains, and he provides a list of all the good things we can eat from those families. He encourages physical activity for health and maintaining lean body mass. All of this is backed by plenty of research, and all of it I agree with. I even agree with the concept of fasting- in that we really shouldn’t be eating all day long. Snacking IS bad, if we want to lose weight. We should give our bodies a rest between meals, so that we can burn those calories, and if we want to lose weight, to burn some fat as well. But do we need to fast for 24, 36, 48 hours? No. We do not, and as was demonstrated in this study, most people would have a hard time sticking to prolonged fasting regimens like that. Will fasting regimens like that result in weight loss? Sure! I have no doubt! And if that’s what works for you, and you find that you can stick to it, then that’s great. But for most of us, it would be very hard, and when taken as a whole, the body of literature to date has not yet shown that those prolonged fasts are superior to other diets (and there are several reviews published). In the end, we are all different, and if we hold to the basic tenets of healthy diet and lifestyle as above, which are the gist of basically every “hot” diet book out there, we will all be fine.

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