Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Intermittent Fasting and Glycemic Index of Foods

  1. Jul 16, 2007 #1

    Simfish

    User Avatar
    Gold Member

    As is demonstrated by research (http://en.wikipedia.org/wiki/Calorie_restriction#Intermittent_fasting_as_an_alternative_approach) , intermittent fasting produces similar results to calorie restriction. However, I have a question here. Are the result of intermittent fasting dependent on the glycemic indices of the foods used? Surely, if foods with high glycemic indices (like refined foods) were used in the diet, wouldn't blood glucose levels just shoot up after the "binge" period?
     
  2. jcsd
  3. Jul 16, 2007 #2

    Danger

    User Avatar
    Gold Member

    I've never heard of 'glycemic index', unless that's a fancy name for the rate at which food is metabolised into glucose. As a former diabetic who still occassionally runs into a hypoglycemic problem if I get too stupid, I know that a steady, moderate intake is the preferred approach. The whole point is to keep the body's glycogen (glucose storage) at a level that can supply glucose to the cells as needed. It's the 'peaks and valleys' that cause the problem.
    Adrenaline will certainly be able to give you a full, proper response. (That's Science Advisor Adrenaline, not epinephrine.)
     
  4. Jul 16, 2007 #3

    Simfish

    User Avatar
    Gold Member

    Yeah, "steady and moderate" does not sound like intermittent fasting (which is more "bingy"). Yet the mice also have enhanced insulin response, which is kind of counterintuitive (unless the foods were of low GI)
     
  5. Jul 16, 2007 #4

    Danger

    User Avatar
    Gold Member

    Well, honestly, I didn't check out your link... so I don't know what happened with the mice. :redface:
    I'll check up on it in a while, but I'm a bit busy at the moment.
     
  6. Jul 17, 2007 #5

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    These are not diabetic models being described, but animals that can normally metabolize glucose. Wikipedia isn't a very good source to use for research. You'd have to dig up the original articles to see what was really done. Without looking at the design of the studies, I wouldn't know if "intermittent fasting" would involve ad libitum feeding during the fed period, or if it was a fixed ration. In terms of the general concepts presented, my understanding is those effects are considered to be due to maintenance of a low body weight, not necessarily any particular glucose level.
     
  7. Jul 17, 2007 #6

    Simfish

    User Avatar
    Gold Member

    http://www.newscientist.com/article.ns?id=dn3668

    http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12724520 => full text

    The question I have relates to insulin spikes that come right after glucose binges.

    The problem is that the methodology does not specify which type of food is used. It's possible that the type of food and the glycemic index associated with such food could affect the body's response to it.

     
    Last edited: Jul 17, 2007
  8. Jul 17, 2007 #7

    adrenaline

    User Avatar
    Science Advisor


    Your question reflects the kind of thinking behind the atkins diet, south beach etc. where their philosophy exploits the theory that glycemic index could be a useful tool in lowering insulin production in non-diabetics — and thus their levels of body fat. I think Barry Sears PHd does the best job discussing this iin his Mastering the Zone books. I trust someone with with a Phd in nutrition and biochemistry over us medical doctors who generally don't have much in depth education in nutrition unless we pursue it independantly. However, these mice studies were not designed to take that into account so you bring up a interesting point.
    .

    In genereral we are taught that risks of diseases such as type 2 diabetes and coronary heart disease are strongly related to the glycemic index of the overall diet. In 1999, the World Health Organization (WHO) and Food and Agriculture Organization (FAO) recommended that people in industrialized countries base their diets on low-GI foods in order to prevent the most common diseases of affluence, such as coronary heart disease, diabetes and obesity.



    The mice studies were looking at overall calorie restriction and or fasting states followed by refeeding and its effect on disease state ( insulin resistance etc.) I don't think the studies looked at the glycemic index of the food ( although I prefer glycemic load). As you bought up, the GI does affect insulin spikes postprandrially ( even in non diabetics) and I am sure would affect post-fast feeding by reducing the amount of post prandial feeding calories ( insulin is a appetite stimulant!) consumed by the mice.
     
    Last edited: Jul 17, 2007
  9. Jul 17, 2007 #8

    Simfish

    User Avatar
    Gold Member

    Yeah - it would be a good idea to ask about this nuance to the researchers by e-mailing them...

    Does anyone know of any other sources I could consult on this?
     
  10. Jul 21, 2007 #9

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    If you follow the sources to the original study, you can find out from that what the mouse chow formulation was. However, I've discussed other studies with people who study nutrition in animals (not these directly) and one problem they have run into in interpreting studies is finding out what the exact diet was. Most report the brand and formulation used, but because these are proprietary information, the manufacturers make it really hard to get details of the sources of the nutrients. All you can find out are things like crude fiber, protein, fats, calories, and certain other nutrients, but not what the source of those nutrients is (i.e., are they using corn or soy). Serious nutritionists will have custom diet formulations made rather than buying commercially available rodent chow in order to specify all of the exact ingredients, precisely for the reason you're asking, and can provide those details upon request. If that wasn't the primary question of the study though, the researchers may not have taken it into consideration. A few manufacturers do realize the need to provide these details for research diets, so do make that available upon request.

    I think I understand what your question is a little better, though. You're wondering if it's not specifically the caloric restriction, but the insulin spikes after re-feeding that are having the benefits, and that seems to be a fair question. Again, I'd suggest trying to locate the original articles. It's hard to measure hormones very often in mice since they have so little blood volume, but it's possible that the study did monitor insulin or blood glucose levels, or other related measures. I think, rather than spinning your wheels looking to find out details on the diet, it would be more useful to look directly for the insulin levels over time in the animals on those diets.

    Also, because I know these types of studies have been misused/ intentionally misinterpreted by some groups to support potentially unsafe diets for people, keep in mind that mice have a very different metabolism from humans, and a much shorter lifespan. Also, rodents in a laboratory tend to get fat on normal diets, so caloric restriction often doesn't mean they are underfed, just that they aren't allowed to get fat eating as much as they want to eat, so that's another reason to carefully read the details of the original study to find out what exactly that group is defining as "caloric restriction." It's not a definition fixed in stone. The same for intermittent fasting...how long, and how accessible was food upon re-feeding? Intermittent fasting could mean anything from "meal fed"...in other words, given 2 or 3 meals a day and no access to food in between meals...to food-deprived to the point of weight loss.

    Food deprivation for even a day in mice has a LOT of other effects aside from just making them hungry or affecting insulin levels. Their metabolic rate is so high that they'll lose a significant amount of weight after just a short fast. Aside from all the changes in the orexigenic and anorexigenic hormones and neurotransmitters, the stress axis is activated, and reproduction suppressed.

    There is an important point to be made from your question, though, and that is that such studies on caloric restriction/fasting are rather blunt tools for looking at what is extending the lifespan of those mice under those conditions. Such conditions effect a large number of changes in multiple systems in the animal, and any one or combination of those could be what is benefiting lifespan. It also does not address whether it is affecting anything other than lifespan. There could be non-lethal conditions that are exacerbated by such a diet, or that are not easily measured in mice, or not measured in these studies. The type of question you are asking is the type of question others should ask too, and probably are, in terms of finding out just what specific thing has changed during these conditions to increase lifespan (and what is the quality of that increased lifespan).
     
    Last edited: Jul 21, 2007
  11. Jul 23, 2007 #10
    Whoa, this topic kind of hit me right between the eyes. I've been researching evolutionary physiology for several years now and this makes perfect sense from that perspective. I'm going to give it a try.

    To answer the OP's questions, yes high GI foods would cause an immediate spike in glucose levels but so what. The fundamental principle here seems to be the precipitous decline in glucose levels triggers new processes in the metabolic axis. Those processes \u aren't \u triggered by highly regular diets.
     
  12. Jul 23, 2007 #11

    DaveC426913

    User Avatar
    Gold Member

    You do realize that, once a Diabetic, always a Diabetic?
    Sounds like you're just very well controlled. Or you've lost a lot of weight.
     
  13. Jul 23, 2007 #12

    Danger

    User Avatar
    Gold Member

    Yeah, I hear that all of the time. I was never on insulin or pills, but a very strict diet (weighing everything within a gram. :grumpy:) If I was 15 minutes late for a meal, I'd go into shock. Then I found out that beer counts as bread on the diet. Working at the bar, I'd be scheduled to eat at 5:00, and was off duty at 6:00... so I'd slug back a beer to keep the levels up until I could get home and eat, rather than pay my 1/2 staff price for a meal. That's when I realized that I'm a natural-born alcoholic. I'd get up to 3 or 4 loaves a day, and not eat at all. I could easily go 3 days on beer alone. The next time that I went for an evaluation, I was clear. Now I eat what I want, when I want, with no complications at all unless I have a heavy sugar intake and then not eat for the rest of the day.
    And if I lost a lot of weight, I'd disappear. My normal weight was 118-120 lbs. I've ballooned to 132 lbs, with my waist size going from 18 inches to 22. I feel like a bloody blimp.
    What really pisses me off is that the diabetes is what cost me my pilot's licence. Now, it isn't even an issue. Not only does it no longer apply, but it is an acceptable condition for a pilot. Unfortunately, there's no way that I can afford to get back into it. It costs at least 10 time more than it did 35 years ago. :cry:
     
    Last edited: Jul 23, 2007
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Intermittent Fasting and Glycemic Index of Foods
  1. Take with food. (Replies: 8)

  2. Absorption of food (Replies: 2)

  3. Heating food (Replies: 9)

  4. Food in space (Replies: 5)

Loading...