The Obesity Code: Can fasting reset your metabolism?

I went to the gym this morning for what my husband calls “double potions” — spin class followed by a muscle-mix session with free weights. His joke is a reference to the class timetable for Gryffindor House in Harry Potter and the Philosopher’s Stone, which included a double-length class for potions once a week.

I know very well that neither physical activity nor calorie reduction, nor both together, are the magical answer for reversing obesity or maintaining long-term weight loss. Those approaches all win in the short term, sure. But then they fail, even after a year or two of diligent adherence because the human body is programmed to return to the previous metabolic set point. I’ve lived the reality of this metabolic adaptation for decades. I’m not obese, but I keep chastising myself about that same 10-15 pounds that I lose and put back on again. I am still looking for an answer to fix things for good.

Can the metabolic set point be reprogrammed?

That’s the million dollar question. I recently read The Obesity Code by Jason Fung, MD. It’s an excellent read and not your average diet book. Dr. Fung is a nephrologist (kidney specialist) and founder of Intensive Dietary Management in Toronto, Ontario, where he specializes in treating people with type 2 diabetes and obesity. I loved his humour and found myself laughing out loud in several spots.

The Obesity Code Jason Fung

Dr. Fung writes that there are multiple overlapping pathways to obesity. The common uniting theme is too much insulin. Obesity is a hormonal disorder of fat regulation. To lower insulin and insulin resistance, we must address both what we eat and when we eat.

Most of the “what to eat” advice sounded familiar:

  • reduce consumption of added sugar
  • increase healthy fats
  • eat lots of the right kind of carbohydrates e.g. vegetables and fruit
  • limit refined carbohydrates
  • choose unprocessed food
  • don’t overdo protein consumption, since protein can also increase insulin, even though not as much as refined carbohydrates
  • maximize protective factors, like fibre and vinegar (Note: I am not sold on the vinegar recommendation.)

But for me, the advice about “when to eat” was new:

  • just don’t snack – “a healthy snack is one of the greatest weight-loss deceptions.” All day grazing leads to constant insulin response stimulation and excess fat storage.
  • make breakfast optional – it’s a myth that we need to eat a hearty breakfast to ensure eating less the rest of the day
  • fasting to create periods of very low insulin are beneficial

Intermittent fasting to combat obesity

Intermittent fasting has been gaining popularity and seems to be working for many people. When we fast, glucose is not available for energy, so the body switches to using fat instead, without any detriment to health. Throwing the switch from short-term glucose burning to longer-term fat burning happens with fasting periods of 24 to 36 hours.

Contrary to what we might first think, fasting increases metabolism: “As food intake goes to zero, the body switches energy inputs from food to stored food (fat). This strategy significantly increases the availability of “food” which is matched by an increase in energy expenditure,” writes Dr. Fung. Studies found that eating a single meal per day led to significantly more weight loss and no evidence of muscle loss when compared to eating three meals per day, despite the same caloric intake.

Your mileage may vary

Throwing my body’s metabolic switch by fasting might just be the magic I’m seeking.

In The Obesity Code, Dr. Fung provides two suggested templates for fasting protocols:

  • 24-hour alternate daily fasting protocol: on fasting days, skip breakfast and lunch and have a light dinner; and eat smart on non-fasting days
  • 36-hour alternate daily fasting protocol: on fasting days, skip breakfast, lunch and dinner; and eat smart on non-fasting days

For both protocols, snacking is prohibited, and it’s important to stay well hydrated with water, green tea, and coffee. Dr. Fung also suggests homemade, salted bone broth in place of lunch on fasting days to maintain sodium levels.

Note that fasting may not be right for you, especially if you have diabetes or a metabolic disorder. If you are interested in making changes to your diet, make sure to have a discussion with your physician or healthcare provider first.

Have you tried intermittent fasting to unlock your obesity code? If so, how has it worked for you? I may give it a try over the summer months.

Check out Caitlin Kelly’s recent excellent post about her fasting experience: The Challenge of Intermittent Fasting.

Further reading:

Fasting Diets Are Gaining Acceptance: Anahad O’Connor, The New York Times, Well. March 16, 2016

Scarborough doctor’s book says insulin makes you fat, fasting makes you thin: Michele Henry, The, January 25, 2016

Intermittent fasting, done right, can lead to weight loss: Leslie Beck, The Globe and Mail, June 15, 2015

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27 Responses to The Obesity Code: Can fasting reset your metabolism?

  1. Srinath April 3, 2017 at 4:12 pm #

    Hello, thanks for your webpage. I may have a unique success story so far, but I also have a problem. I essentially fasted my way down almost 100 lb. 238 to 140 when fasted for 8 days, but eating one meal a day, I’m closer to 150. Now being 5′ 9.5″ and male with medium/small frame I now am in the underweight category even @ 150. Insulin sensitivity, and all other biomarkers markedly better, by miles, not even a little. I went from dangerous to professional athlete category in a matter of months. Essentially I’d eat 1 meal and go for days with nothing but water black coffee/tea. And repeat. My longest is 20 days. But I did several between 2 and 10 days too. However, even @ 140 lb, I had a few handfuls of fat I could grab around my belly. Atleast a few lb worth. I want to get rid of that. I can fast more, however Since Jan 13th (the day I got to 140) I have fasted a good bit, and that fat has not moved. I have worked out and muscled up, fasted and slimmed down, and the grabs of fat have stayed. Could there be something else ? Hopefully I don’t need to fast 20+ days again.

    • Jane April 3, 2017 at 8:06 pm #

      Hi Srinath,
      Thanks for your comment. Unfortunately, I cannot recommend different fasting schedules or body weight targets. You should consult with your physician to take them through your progress and make sure you are maintaining a healthy weight for your height.

  2. Brenda March 22, 2017 at 4:35 pm #

    I don’t think it’s helpful to “feel starved” & be upset about that. Pack a small piece of fruit for when you know you’ll be tempted. As long as it’s “real” food, it should be fine. I will sometimes have 1/2 avocado or 1/2 banana if I’m really hungry. I load up on liquids 1st but then go to food as dinner approaches. I can’t imagine ever going back to 3 meals/day – it’s way too much food!

    Thanks for writing this! All the best!

  3. Celia March 22, 2017 at 9:42 am #

    I have tried the intermittent fasting for a week (3 days total fasting) and each time I am feeling more hungry. The first time was pretty easy. Woke up today hungrier that the last time (day before yesterday). Been drinking water and broth as suggested in the Obesity Code. Anyone having this problem and if so any solution?

  4. Kim March 9, 2017 at 7:43 am #

    Hey Jane;
    I’m 53, what most would call “very fit” and active and also a really healthy eater. I couldn’t labor through most of Dr. Fung’s book because most of it was review, however the last bit about fasting was awesome. The parts that resonated with me was that hunger drops off after day two and growth hormones kick in after longer fasts. I’d done 16 hour IF for months with zero benefit and some circadian upset. I’d done a few 24 hour fasts with just a little diluted juice and they were MISERABLE (likely because the tiny amount of juice caused a slight bump in blood sugar). In Jan I did a Whole30 and lost a whopping 0.6 kg. The owner of the gym where I train did a 5 day fast, I thought she was insane. She said it wasn’t bad! I decided, “what the heck?” and jumped in pretty much on a whim. I’ve been fasting for 3.5 days and I feel awesome! I’d love to know if your readers have done longer fasts.

  5. Jim Brodbeck February 18, 2017 at 6:28 pm #

    Hello. I have read the Obesity Code and it seems to explain everything I have been through over the years. My wife and I have lost 45 lbs over the last 1 1/2 years by eating a low calorie diet. We are now struggling to keep from gaining even though we are eating about the same. I am 71, 5′ 6″, 190 lbs and want to loose another 25 lbs. We are starting to phase in Dr. Fung’s plan and are now at least plateauing and hope to start loosing again.

    How long does it take before our set points lower enough help keep the weight off? Or well we have keep intermittent fasting apart of our eating for the rest of our life?

    Thanks for your time.

    • Jane February 22, 2017 at 9:39 am #

      Hi Jim,
      Congrats on your weight loss successes! From what I’ve read, plateaus are common and any habits that helped achieve the weight loss need to be sustained over the long-term in order to keep the weight off. I don’t know how long it takes before set points adjust for good or if that’s possible. I suggest you contact Dr. Fung and ask him if there are long-term studies that might provide an insight.

  6. Patrida Sutton February 14, 2017 at 6:08 am #

    Hi Jane,

    After years of yo-yo dieting I finally stumbled across The Obesity Code last year and have been following a range of different intermittent fasting regimes for one year now, I’m 44, I have PCOS and had insulin resistance. Through Intermittent fasting I have lost 58lbs, I aim to lose another 45lbs this year, all my blood test results are now within the normal range and this has become an enjoyable and long lasting way of life for me. I’ll never go back to “3 square meals” a day. Nothing compares to the benefits of intermittent fasting.

    • Jane February 16, 2017 at 8:45 am #

      Glad to hear you have found success with intermittent fasting, Patrida.

  7. Todd January 3, 2017 at 11:37 am #

    My parents, both almost 70 and type 2 diabetics, introduced me to this book. They have both been on so many diets over the years that I typically hear them excitedly describe the latest fad they’re following and I internally glaze over and roll my eyes. As with so many diets they’ve tried, they lose 10 or 20 pounds only to see it come right back within a few months. And with no change in the status of their diabetes! When I first heard them describe Dr. Fung’s book, I had the same lackluster response. However, after months of watching my parents follow Dr. Fung’s recommendations, I noticed a difference vs. other diets. I watched my parents lose 10’s of pounds each and COMPLETELY eliminate their need to take daily insulin. Wow. In my case, I’m a healty 40 something. I exercise every day and have done so for years – running, endurance biking, hockey – mixture of light and intensive workouts. Despite the work I put in, I have always struggled with an extra 20-30 pounds of weight that I could sometimes temporarily shed, but would always return. That extra weight mystified me – made no sense in context of my exercise regimen and perceived good dietary habits. I resolved to give Dr. Fung’s book a read and implement his recommendations to see if my non-diabetic response might mirror my parent’s experience. The results have been fantastic. Breakfast. Never liked the meal anyway, I typically ate it because I believed it was a necessary meal to start the day. With intermittent and 1-2 times per week 24 hour fasting, I lost the 20 pounds I’d struggled with for years – and have kept it off. My entire appearance is leaner and I feel healthier than ever. As Type 2 diabetics, the book’s recommendations were nothing less than miraculous for my parents. For a healthy 40 something like myself, the results have also been beyond my expectations. I now treat the book like my dietary bible (the changes in eating, and not eating, are EASY to implement). If you’re not in one of the high risk categories where you need to consult a physician, give Dr. Fung a try.

    • Jane January 3, 2017 at 12:46 pm #

      Thanks for sharing your experience and your parents’ experiences following Dr. Fung’s recommendations.

  8. j James October 9, 2016 at 8:42 pm #

    Hey I don’t think you understand the program , this was created by Dr.Fung to fix diabetes or a metabolic disorder, polycystic ovarian syndrome, kidney issues and obesity in general, fatty liver , high blood pressure etc.

    it works fantastically, however you need to go through the program by referral of your doctor- To see Dr. Fung

    • Jane October 16, 2016 at 8:55 pm #

      Thanks for your comment. I do understand that Dr. Fung has had success using a fasting program to treat people with diabetes and other metabolic disorders. As I am not a doctor, I will only say that anyone interested in this approach should speak to their doctor about whether this program would be right for them.

    • jonny December 28, 2016 at 1:24 am #

      First of all most of what Dr.Fung says is theory and just as any diet it will differ individually and has to be evaluated over time. I can only warn of any hype, just because he is convincing to a laymen. And yes, combining low carb and and fasting is just another diet, and no, his approach to put type 2 diabetics on a diet isnt new, it’s standard procedure.
      2nd of all, all that is said about diabetes refers to type 2 diabetes. Type 1 diabetes has only one solution and that is exogenous insulin for life and fasting will potentially kill you.
      Concerning diabetes type 2, you’re right to a degree and wrong at the same time. Dr.Fung promotes his dietary approach as anti-diabetic (it may or may not be). However one thing is certain: once your type 2 diabetes has advanced so much that your pancreas cant produce adequate levels of insulin anymore (resp. your functional beta cells are highly reduced), fasting can be fatal.

  9. Karen Nygard October 7, 2016 at 1:56 pm #

    I’ve been following Dr.Fung’s program for about 6-7 weeks now, doing 3 x 24 hour fasts a week and then eating low carb the rest of the time, with the odd Saturday indulgence. I’ve lost 12 pounds, 5″ off my waist, and I’m off my Metformin for type II diabetes with a steady, gradual drop in my blood sugar even off medication. I find I have lots of energy for workouts at the gym and feel generally better and more energetic. Hopefully the trend will continue!

  10. JEAN September 22, 2016 at 5:38 pm #

    I have read his book and studied intensively fasting and intermittent fasting, Im type 2 diabetic and dove right in to stop my insulin , it took only 2 weeks to get off of 75 units a day. The only danger was from the insulin and having to low a blood sugar , that is easily solved by stopping insulin as insulin does not help the disease but lowers blood sugar only, while the disease progresses at the same rate as someone that didn’t take any meds. The danger is to type 1 diabetics not type 2 if they stop insulin. Its amazing how quick this disease that I have been fighting for over 17 years has regressed. The first 4 days I was sluggish then all of a sudden I got this burst of energy where I couldn’t sit still for more than a few minutes, I was able to complete long term projects within hours.My weight has not fluctuated a lot which probably has to do with the fact that Im farely skinny and lean for a 6foot 1 at 193 lbs.

    • Jane September 27, 2016 at 11:59 am #

      Hi Jean,
      Thanks for sharing your experience. I’m glad to hear about your condition improving. I recommend that anyone with type 1 or type 2 diabetes should speak to their physician before trying any fasting strategy.

  11. Dianne September 8, 2016 at 11:28 am #

    Fasting doesnt seem to help me. I’ve been lowcarb for over 2 years. Ive lost a significant amount of weight. My diabetes is now controlled without medication. Blood sugar and blood lipid tests are vastly improved. But I find extreme loss of strength when fasting. If I fail to eat for 18 hours even regular exertion such as lifting 50 lb bags. Or even cutting the grass becomes very hard for me to do. Im normally a strong woman who has no problem with these tasks.

    • Jane September 13, 2016 at 12:53 pm #

      Congrats on the weight loss and controlling your diabetes without medication. Fasting is not recommended for people who have diabetes or troubles managing blood sugar. You have achieved impressive results on a low-carb diet and maintained that for two years, so you have found a good, sustainable solution that’s working well. Good stuff!

  12. Rachel Moody August 11, 2016 at 12:55 pm #

    Hi Jane
    I am curious to see if you have tried doing any fasting??? I have been low carbing with fasting off and on since MID JUNE which has resulted in 10 lbs lost. I struggle with 20 lbs or so off and on.
    Just wondering if you have had any success?

    • Jane August 16, 2016 at 9:41 am #

      Hi Rachel,

      I tried fasting a few weeks ago but found that it upset my circadian rhythm. I skipped breakfast and lunch and had a good dinner, but was wide awake in the middle of the night, Which can happen for other reasons, so I may try again in the future. Your results are encouraging!

      As a compromise, in the last couple of weeks, I have been skipping breakfast. Not much movement on the scales, yet, but hope springs eternal.

  13. Luigi June 2, 2016 at 10:08 am #

    I just put this book on my recommended reading list, Jane.

    What does Dr. Fung have to say about eating to recover energy after a hard workout? By “hard workout” I mean things like hockey or stair training (on real stairs, not a machine in a gym).

    • Jane June 2, 2016 at 10:26 am #

      I think you will enjoy the book, Luigi. Dr. Fung answers questions about fasting in Appendix B. For the question, “Can I exercise while fasting?”, he says, “Absolutely. There is no reason to stop your exercise routine. All types of exercise, including resistance (weights) and cardio, are encouraged. There is a common misperception that eating is necessary to supply ‘energy’ to the working body. That’s not true. The liver supplies energy via gluconeogenesis. During longer fasting periods, the muscles are able to use fatty acids directly for energy.”

      He goes on to say that bodybuilders are taking a greater interest in working out in the fasted state to promote muscle growth through boosted growth hormone which also happens during fasting. He warns, however, that people with diabetes must take special precaution because their blood sugar could dip dangerously low and outlines separate recommendations for them.

  14. Caitlin Kelly May 16, 2016 at 4:48 pm #

    Thanks for the link!

    One of the most compelling insights I’ve gained from intermittent fasting is how little, really, we need to eat.

    I do love a great meal! I love a cocktail.

    But today — a “feast” day — my stomach rebelled (as it’s now prone to do) if I eat the way I did before. Lunch today was a small soup, pork souvlaki w spinach and salad, 2 small slices of pita w hummus, water and (yes!) dessert and coffee.

    That is a lot of food…compared to what I’ll be eating tomorrow.

    I now see what this does to my body and how it (now) rebels. It’s all…instructive. 🙂

    • Jane May 16, 2016 at 5:14 pm #

      Thanks for sharing how it’s working for you, Caitlin!

  15. Theresa Lemieux May 16, 2016 at 1:23 pm #

    Jane, I’ve tried intermittent fasting, and I always feel better. I don’t know it it’ self-control, if it’s all in my head – it’s not always easy, but it’s always easier than I think. Maybe it’s some post-gluttony guilt relief – like paying an indulgence to the God of Fitness. I’ll give this book and read and try fasting. My only concern is encouraging an eating disorder in the teens in my care. But nothing like information to quell fear.

    • Jane May 16, 2016 at 2:22 pm #

      Thanks, Theresa. I share your concern about over-control of food intake. I think the key is to know ourselves and figure out what will work for us personally and safely. I found other ideas beyond intermittent fasting insightful too, such as cutting down on snacking, or just skipping a meal if I’m not hungry.

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