Nov 23, 2007

One meal each day vs. intermittent fasting

People in the intermittent fasting group on Yahoo are trying out many variations of intermittent fasting. The most popular appears to be daily (or frequent) fasts of greater than 18 hours, without caloric restriction. This normally means following the Fast-5 program of eating all food within a five hour window each day. The Fast-5 approach avoids longer fasts, but provides many more of them. Following this approach, one is fasting most of the time. There has been little scientific data on the relative benefits of different variants of intermittent fasting, so many of us are keen to learn which provide the greatest benefit. Indeed, some remain unconvinced that intermittent fasting provides any benefit at all.

The Mattson group has just published a study of the effects of reduced meal frequency on glucose regulation (Carlson et al. 2007, Metabolism 56:1729. "Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women"). They found that people on a diet that involves a single meal each day show elevated fasting glucose levels and impaired glucose tolerance. This is in contrast to an earlier study (Johnson et al. 2007, Free Radical Biology and Medicine 42:665) that tested alternate day calorie restriction and found improved diabetes risk profiles (also see the Johnson upday downday diet, which is promoted by the same James B. Johnson). The authors suggest (in the Carlson et al. paper) that the key difference is an overall reduction in energy intake.

That may be true, but there are two other important differences between the Fast-5 approach and alternate day fasting (including my method of fasting three times each week from dinner one day until dinner the next day, which is less rigorous than a full bedtime-to-waking fast of 30+ hours). First, even a dinner-to-dinner fast is longer (roughly 23 hours, on average, as opposed to 19 or 20). If the benefits of fasting kick in after 12 hours or so, this difference could be more significant than one might otherwise think. Second, the consumption of all daily calories within a five hour window is very intense, and ad lib eating over 24 hours need not be. Between fasts I usually eat dinner, a late-night snack, breakfast, lunch and dinner. Less intense eating means less insulin secretion and less food in the stomach at the beginning of a fast, which would further increase the effective length of the fast.

Perhaps the longer fasts are more effective. Further research will tell, and it's being done.

5 comments:

q said...

Thanks for this blog. There are too few good sources of information regarding I.F. I look forward to your updates.

JohnN said...

I encourage fasters to ignore the Mattson's conclusion.
Rising fasting blood sugar in this case should not be interpreted as an unfavorable change in diabetes risk profile - far from it.
Without food intake the body must switch to internal fat storage for as fuel and save the hepatic glucose production for the brain (peripheral muscles withdraw their glucose transporter and use ketones instead). You would expect blood glucose to drift higher until brain activities begin after the first cup of coffee or after the morning break whichever comes first.
The health benefits of fasting come from the reduction in circulating insulin (the source of many metabolic diseases), clean-burning fuel in the form of fat and others.
It's unlikely that the FBG will rise above 125 or so when insulin response will kick in. Note that this level is the same as the post-prandial.

Kayaman said...

I don't think we should ignore any scientific research, so long as it was done honestly and the results are accurate. Interpreting the data can be done in many ways, however, and is often influenced by our pre-existing beliefs.

What this study tells me is that eating 300g of carbs for dinner is bad for you, and if you wake-up and take a gtt, it's not going to be good. No kidding?? But what about the lowered TG in the ompd subjects - why isn't that mentioned?

JohnN said...

To kayman,
Please reread my comment. The conclusion is false. In the diabetic world, fasting blood sugar is the last one to succumb since the body has the entire night without food intake to secrete insulin and still could not drive FBG down.
For low-carb eater, you are burning ketones, insulin level is low, the glucose is beinng reserved for the brain.
DM (itout bias) should be defined as the body's inability to control blood sugar despite high insulin production.

Kayaman said...

John,
I've reread your comment, per your request.

"I encourage fasters to ignore the Mattson's conclusion"
What conclusion? I don't see any (in the abstract), but simply a statement of facts of what they had observed. And I believe they did not lie or fudge the data.

You say: "Rising fasting blood sugar in this case should not be interpreted as an unfavorable change in diabetes risk profile"
But your first argument here is not valid: "Without food intake the body must switch to internal fat storage". This is a true statement out of context, however it's not relevant to this study: Both groups were on an isocaloric diet, and in the morning when the tests were administered, the OMPD group's livers were full of glycogen. Also, when consuming high levels of carbs, the body's expression of fat burning enzymes is depressed, so I'm not sure they ever really "switched to fat as fuel". I'll bet their livers were cranking out the glucose during the day, and getting much of the substrates (for gluconeogensis) from skeletal muscle (very bad indeed).

Second argument: "You would expect blood glucose to drift higher...". I would not expect this. For example, why didn't the TMPD group experience this morning elevation? I certainly don't. But I know a diabetic who does.

Third: "The health benefits of fasting come from the reduction in circulating insulin, clean-burning fuel in the form of fat and others". I agree 100%. However, I'd argue the OMPD subject were not really fasting, and never got a chance to use the 'clean-burning' fat to the degree you claim. Instead, the negative effects of consuming 300g of carbs at once outweighed any benefits they got from their 'fast' as was evidenced by their elevated morning glucose levels and impaired GTT.

And from your response-post: "In the diabetic world, fasting blood sugar is the last one to succumb since the body has the entire night without food intake to secrete insulin and still could not drive FBG down."
This statement directly contradicts your first argument:
"Rising fasting blood sugar in this case should not be interpreted as an unfavorable change in diabetes risk profile"

What this study reveals is that if you're going to consume carbohydrate in your diet, you should spread it out over the day. Its analagous to having to drink a bottle of poison: you wouldn't want to drink it all at once, but rather over a period of time. This will minimize the negative effects.