Why obese people can't fast

Why do obese people claim it is impossible to fast?

Most overweight people are terrified at the prospect of facing any period of time without ready access to food. Persuading them to begin a program of intermittent fasting is a hopeless cause. They just refuse.

Contrary to popular opinion, this is not just glutonny at work. It is the effect of what I call "the cycle of hunger," the 2-hour up and down cycle of rising sugar and insulin, followed by their inevitable fall. The precipitous fall of sugar and insulin triggers mental fogginess, fatigue, and insatiable hunger. (By the way, this is the same phenomenon underlying the silly notion of "grazing.")

According to an LA Times article, fasting may be difficult to impossible for some people:

"Ruth Frechman, a registered dietitian in Burbank and spokeswoman for the American Dietetic Assn., says she frequently sees such extreme strategies backfire. 'You're hungry, fatigued, irritable. Fasting is not very comfortable. People try to cut back one day and the next day they're starving and they overeat.'"
(Not surprising, coming from the American Diatetic Assn. They, along with such agencies as the American Diabetes Association, are vocal proponents of low-fat, high-carbohydrate, "healthy whole grain" diets--you know, the diets that make us fat and diabetic.)

Ms. Frechman is correct: Having someone engage in a period of fasting, no matter how brief, when the diet leading up to the fast is filled with "healthy whole grains" and other carbohydrates will result in painful hunger that eventually overcomes any effort. A period of overeating typically follows the aborted attempt.

Fasting cannot work as long as the 2-hour cycle of hunger continues. The first step: Eliminate the 2-hour cycle of hunger by dramatically reducing or eliminating carbohydrates. Our preferred method is to eliminate wheat, cornstarch, and sugars. (Just be aware of wheat withdrawal, the fatigue that develops in the first 5 days after wheat elimination that affects up to 30% of people.)

Once wheat, cornstarch, and sugars are eliminated, hunger reverts to that of physiologic need--appetite will be smaller and less intense, since it is driven by your body's needs, not by abnormal stimulation from wheat, cornstarch, and sugar. The fear of not having food dissolves, the 2-hour cycle of mental fogginess, fatigue, and hunger will be gone.

Intermittent fasting is a wonderful strategy for reducing weight; gaining control over lipids, lipoproteins, and coronary plaque; regaining appreciation for food; reducing appetite. But it's not even worth trying unless you've already eliminated the unnatural appetite triggers that will booby-trap any fasting effort.

Comments (21) -

  • Anonymous

    9/9/2009 12:21:40 AM |

    I agree with your post.
    Once you are adapted to a low carb diet Intermittant Fasting becomes really easy and you feel great without becoming hungry or mentally foggy. I wouldn't dream of trying IF on a high carb diet since it would be like self torture.


  • rfrancis

    9/9/2009 12:47:06 AM |

    Dr. Davis,

    I agree with you as far as this goes -- but I'd go a bit further.

    For those (myself included) who are substantially insulin resistant, and in particular type II diabetic, even years of a low carb diet may not beat the hunger cycle, very possibly (c.f. Gary Taubes and others) because that very insulin resistance interferes with the release of stored energy, ensuring that the insulin resistant person becomes hungry again every time they've exhausted (or worse, stored!) the energy obtained from their last meal.  Feelings of muscular tiredness, lethargy, even mysterious panic -- I doubt anyone chronically obese is strangers to some or all of these.

    Of course, even so, the first step is exactly as you say.  As for what comes next... I'm all ears. Smile  Personally, I'm trying to get my physician to at least investigate possible connections between subclinical hypothyroid and insulin resistance...

  • Stan (Heretic)

    9/9/2009 1:36:01 AM |

    Anonymous wrote: "Once you are adapted to a low carb diet Intermittent Fasting becomes really easy and you feel great without becoming hungry or mentally foggy."

    Absolutely!  On a high (animal) fat diet, our metabolism is identical to a fasting metabolism, therefore there is no noticeable change in feeling, stamina, not much hunger even after a couple of days!  There isn't much need to drink water either, since fat burning produces water.   Also we typically eat only one meal a day - that is completely sufficient without any need to snack.


  • Ross

    9/9/2009 3:07:45 AM |

    Very similar to my own experience.  I used to try fasting, as my very liberal friends used to tell me that it's great for "purification" and "detoxification", but I couldn't hack it.

    Now I do a 36 hour "after dinner to before breakfast" fast about once a week (on random days of the week to shake things up) and the strongest symptom I have is during the afternoon and evening of the fasting day I get very mellow and relaxed.  I also feel small hunger pangs as I go to bed and that's about it.

  • Andrew

    9/9/2009 3:13:16 AM |

    gft chromium helps with fat metabolism

  • Rick

    9/9/2009 5:37:00 AM |

    Dr. Davis,
    Could you expand a bit on what you mean by the 2-hour cycle?

  • Lincoln

    9/9/2009 7:55:10 AM |

    This is a really good article which clearly explains the concept of the hunger cycle.  From my experience if people are particularly insulin resistance then a longer lead in time of gradually reducing carbs helps the body to adjust.  Then it is possible to include a period of fasting.



  • Daddy

    9/9/2009 9:23:47 AM |

    I have only recently started in with the low carb diet.  I was curious if there is any knock against dairy too.  Thanks!

  • Methuselah

    9/9/2009 11:49:19 AM |

    Your article makes perfect sense, but the title is a little misleading. Clearly once an obese person has removed the 'unnatural appetite triggers' they will be able to fast as comfortably as a slender person who has eliminated those triggers. Indeed an obese person who has emiminated the triggers might be more able to fast than a slender person who has not.

  • Dr. William Davis

    9/9/2009 12:11:18 PM |

    Hi, Rick--

    After a carbohydrate load, blood sugar (glucose) increases sharply, followed by insulin. In response to insulin, blood sugar drops precipitously, often to levels below normal. This is where all the symptoms like mental fogginess develop.

    The entire cycle requires 90-120 minutes or so, depending on the foods consumed, the mix of foods and food types consumed, and individual responsiveness.

    Interestingly, of all foods, wheat triggers the fastest and highest glucose peaks, even compared to table sugar (sucrose).

  • Susan

    9/9/2009 1:03:31 PM |

    One thing you find when you go wheat-free (let alone low carb) is how difficult it is to buy anything for lunch that isn't wheat based. The great thing about IF is that it frees you from the endless repetition of "chicken caesar salad, please, hold the croutons and bacon bits." (Bacon bits are out because they're usually fake.) In fact, after a couple of days, you  can walk through a food court, and your only reaction is to marvel that all of these people are eating lunch, which is totally unnecessary. The other thing about IF is that it also makes it easier to say no to snacking or other mindless eating.

  • Anonymous

    9/9/2009 1:57:38 PM |

    I just want to know how all of you take your vitamins and other pills on an empty stomach?  I would vomit them right back up!

  • Gretchen

    9/9/2009 3:17:38 PM |

    It's not just "mental fogginess, fatigue, and insatiable hunger" that is the problem. When I was prediabetic and trying to lose weight, I had difficulty going on a diet because when I cut back on my food intake, I'd get what I now know are symptoms of hypoglycemia.

    I actually enjoyed being hungry, because it told me I was eating less than I needed.

    What I couldn't tolerate was "the shakes," accompanied by a feeling of panic that if I didn't eat immediately I'd die.

    Because many overweight people are also prediabetic, they probably have the same symptoms of hypoglycemia, caused by "too much insulin, too late."


    9/11/2009 11:20:13 PM |

    As a former Fatty, I can understand the difficulties some would have with Intermittent fasting. Two points:  don’t start here. I managed to control my carb carvings first with Atkins, then was able to move on to Intermittent fasting when I was ready.
    Second- I don’t like that Ruth Frechman calls IF an “extreme strategy”- it just might be the healthiest Life Saver going.

  • Dr. William Davis

    9/12/2009 12:28:48 AM |


    I agree wholeheartedly.

    It shows how far our diets have drifted from the physiologic ideal when we have to shift away from it in steps!

  • PJ

    9/22/2009 2:41:42 PM |

    Um. I weigh about 380 and I have no trouble fasting. In fact it's 9:39am here on a Tuesday and the last time I ate was Sunday around 9pm. This is not because I was doing it on purpose (though I could retroactively assign some glorious reason to it I suppose), but because I'm painting my kitchen so making food was a pain in the butt and I didn't feel like it.

    However when I'm eating highcarb, going without food is horribly hard. The fact that I eat lowcarb is probably what makes it possible for me.

  • Matt Metzgar

    9/27/2009 6:19:05 PM |

    I agree completely with this.  If a person hasn't made the metabolic shift to fat-burning, then fasting will be painful.

  • trinkwasser

    10/2/2009 3:31:09 PM |

    Another "me too": my pattern was high BG at around 1 hour postprandial, returning to normal at two hours and dipping significantly below normal at three or more hours.

    This improved markedly with carb reduction, but I still needed to snack, until I started replacing those "heart healthy" Omega 6s with saturated fat.

    Getting the correct macronutrient balance *for me* lets me routinely go about six hours between eating, whatever my activity level, and those 14 hour fasts for blood tests don't have the response they used to cause.

    I'm still somewhat leery of fasting for that much longer though, as the resulting hypo symptoms and ensuing BG swings as my liver overcompensates are Not Nice and I don't want to push things so far that I restart this phenomenon

  • buy jeans

    11/3/2010 8:26:17 PM |

    Intermittent fasting is a wonderful strategy for reducing weight; gaining control over lipids, lipoproteins, and coronary plaque; regaining appreciation for food; reducing appetite. But it's not even worth trying unless you've already eliminated the unnatural appetite triggers that will booby-trap any fasting effort.

  • Jessica

    3/7/2012 6:56:48 PM |

    I''m fat.  I''m 245 lbs which is considered small on the morbidly obese scale, but still morbidly obese.  I have fasted a day at a time, every other day in prep for my 7 day trial.  I am starting my 7 day today.  Hopefully I don''t s**t the bed on this one.  I''m tired of being a fat ass, literally.

  • Gene K

    3/8/2012 7:20:10 PM |

    You may find the blog of Dr Jack Kruse useful, especially this post - http://jackkruse.com/my-leptin-prescription/. Definitely read all comments, and try to read as many of his other leptin-related posts as possible.