Monday, August 11, 2014

Slow versus slow-brisk walking: Effects on type 2 diabetics


I am not a big fan of reviewing new studies published in refereed journals, particularly those that make it to the news. I prefer studies that have been published for a while, so that I can look at citations to them – both positive and negative.

But I am making an exception here to a study by Kristian Karstoft and colleagues (the senior author is diabetes researcher Thomas Solomon: ), accepted for publication on 30 June 2014 in the fairly targeted and selective journal Diabetologia (full text freely available in a .zip file at the time of this writing: ).

This is a small study. Individuals diagnosed with type 2 diabetes, and who were not being treated for the condition, were allocated to three groups: a control group (CON), an “interval” walking group (IWT), and a slow walking group (CWT).

The groups had 8, 12, and 12 people in them, respectively. Those people in the IWT group alternated between walking briskly and slowly for 1 hour five times a week. Those in the CWT group only walked slowly. Those in the CON group supposedly did not do any targeted exercise.

One of the interesting findings of this study was that there was no difference in terms of health effects between the CWT and the CON groups. The only group that benefited was the IWT group. That is, those who alternated between walking briskly and slowly benefited in a way that was observable from the exercise, but those who walked slowly did not.

This study highlights two facts that I have mentioned here before, but that are often overlooked by those who suffer from type 2 diabetes or are on their way to developing the condition. They refer to visceral fat and are listed below. Visceral fat accumulates around the abdominal organs ().

- Type 2 diabetes is strongly associated with visceral fat accumulation, and is somewhat unrelated to subcutaneous fat accumulation (see the case of sumo wrestlers: ).

- Visceral fat is very easy to burn via glycolytic exercise, but does not seem to respond well to non-glycolytic exercise.

Glycolytic exercise burns sugar stored in muscle, in the form of glycogen, while it is being performed. This form of exercise raises growth hormone levels acutely. Weight training and sprints are types of glycolytic exercise, which also takes other names, such as glycogen-depleting and anaerobic exercise.

Often one sees prediabetics and type 2 diabetics avoiding this type of exercise because it pushes their blood glucose levels through the roof. That happens, however, only during the exercise. After, the benefits are tremendous and appear to clearly outweigh the possible problems associated with the temporary exercise-induced hyperglycemia.

Take a look at the last line of this cropped version of Table 1 from the study, shown below. The relevant line for the point made above is the one that refers to visceral fat volume. As you can see, those in the IWT group had the greatest reduction in visceral fat. This was also the only statistically significant reduction among the three groups; according to an analysis of variance (ANOVA) test, the probability that it was due to chance was lower than one tenth of one percent.



The ANOVA test is "parametric", in the sense that it assumes that the data is normally distributed. However, the authors did not report conducting a test of normality. Also, the sample is very small. Given these, "non-parametric" tests, such as multiple one-group-two-conditions tests run with WarpPLS (link to specific page of the .pdf file of a relevant academic paper: ) would not only be more advisable but also provide more much more information to readers.

If you compare the line showing visceral fat with the other two above it, within the body composition section of the table, you will notice another interesting pattern. In the IWT group the changes in average total body mass and total fat mass were also the greatest, but the largest change in percentage terms was the one in average visceral fat mass. Visceral fat mass is often correlated with total fat mass, with this correlation being a function of how sedentary individuals are, and it does not take a lot of it to cause serious problems.

Sumo wrestlers tend to have large ratios of total to visceral fat mass. Virtually all of their body fat is subcutaneous. They also carry a lot of muscle mass. They achieve these through intense glycolytic exercise alternated with periods of rest and consumption of large amounts of calorie-dense food. To these they add another ingredient - exercise in the fasted state, usually in the morning prior to a large breakfast. Exercise in the fasted state seems particularly conducive to visceral fat mobilization.

By the way, sumo wrestlers consume enormous amounts of carbohydrates, but as noted by Karam () have "low visceral fat, absent hyperglycemia and absent dyslipidemia despite massive subcutaneous obesity".

In my opinion the folks in the study by Karstoft and colleagues would have benefited even more, possibly a lot more, if they had alternated between sprinting and regular walking.

15 comments:

Anonymous said...

Hello Ned,
Just had some questions concerning visceral fat loss - I've been practicing intermittent fasting,but only upto 10 hours,5 hours into the fast,supplementation with 500 mg of niacin,then resistance exercise after the 10 hr mark -
do you think this will aid optimum GH production,as your posts mention supplementation with 1 g of niacin or more.
Additionally,do you think fasting,strength training and niacin will enable GH production to a greater extent than doing any 2 together?
or is it advisable to split up the supplementation without fasting on the other weekdays >?
Thanks for any feedback!

Ned Kock said...

Based on what we know so far, niacin will increase the magnitude of acute GH release when combined with exercise. As you noted, there are several posts here on the subject.

Just keep in mind that IF leads to increases in both GH and cortisol levels, and cortisol is a testosterone antagonist. The post below may be useful:

http://healthcorrelator.blogspot.com/2014/03/should-you-do-resistance-exercise-to.html

If your goal is muscle gain, keep in mind that GH per se doesn’t accomplish much without testosterone. The highest levels of GH are found in young women, who don’t gain muscle mass easily.

But GH seems to be a powerful health-promoter (if it is not a marker of health). The closest to indestructible in the human species is a young woman.

Ned Kock said...

PS: I mean instant-release niacin, the one that causes the flush, in my comment above. I would not recommend more than 1 g per day of it, and even at this level it should be considered an unnatural addition to anyone’s diet. There is no way one can get 1 g of niacin per day through the consumption of unprocessed or minimally-processed foods.

Anonymous said...

Ideally how long should one wait after intense exercise[glycogen depleting] to consume food - so that it does not interfere with the GH spike?
We'd expect to wait until the GH levels dip in the blood - how long a time do you suggest would be most beneficial?

Ned Kock said...

There is a significant drop in GH within 1-2 h after intense exercise. Taking IR niacin makes a difference in terms of both the magnitude of the GH response and the amount of time it takes for it to go back to rest levels. See this post:

http://healthcorrelator.blogspot.com/2010/06/niacin-turbocharges-growth-hormone.html

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Peter said...

How can I tell which kind of fat I have?

Anonymous said...

Is it advisable to supplement niacin at nights after intense exercise?Do you think there will be a down regulatory response to the bodies own GH production?

Additionally just to clarify,is the bump in GH secretion after consuming niacin[without exercise] higher than during deep sleep [ as mentioned in one of your posts]
"Let me emphasize that the peak growth hormone level achieved in the second sprint is about the same you would get without exercise, namely a bit more than 20 micrograms per liter, as long as you took niacin (see Quabbe's articles at the end of this post)"

Ned Kock said...

Hi Peter. See this post:

http://bit.ly/pJxgLH

Ned Kock said...

Hi Anon. What is your goal with taking IR niacin?

Anonymous said...

Hi Ned,
Thanks for the reply!

Truth be told,enhanced Fat loss would be the main objective of taking IR Niacin
Trying to understand on what to do[ or not to do] immediately after the exercise session,that will not negate the effects of peak GH secretion
Cannot find any blog posts to this end.

Ned Kock said...

Anon, about 20-min of brisk walking after a workout would probably do more for almost anyone in terms of fat loss than IR niacin, IMHO.

Eventually you will have to negate GH by raising insulin via protein and/or carb. ingestion. Insulin stimulates muscle growth – it is an anabolic hormone.

Taking in more protein overall in your meals, and reducing other macros, tends to also lead to fat loss with muscle gain, or at least without muscle loss.

This leads over time (weeks) to a caloric deficit which the body is likely to react to. The sustained deficit can be reversed through a “cheat” day where one eats way more calories than normal.

This avoids a metabolic slowdown, which the body often induces via a reduction in circulating thyroid hormones.

Jim said...

Hi Ned,

Not your study of course, but it would have been nice if the authors had extended the time period of the study to get to some steady state weight/fat-total/visceral-fat.

All sorts of physiology changes during changed conditions, the long term values are what count.

Ned Kock said...

Hi Jim. I agree. Compensatory adaptation at work:

http://healthcorrelator.blogspot.com/2010/06/compensatory-adaptation-as-unifying.html