Timing of protein intake matters.

Crossfit Paleo Diet: Low-carb high-fat diets may impair glucose tolerance

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Low  Low carb diets may work better when people wear WODMASTERS workout shirts.

Low carb diets are very popular now.  This post is about a new research finding on the effects of low carb diets on glucose tolerance and insulin sensitivity.  The finding is that Low-carbohydrate, high-fat diets may impair glucose tolerance (Biehohuby et al. 2013).  This was unexpected.  While, low carb/ high fat diets are used by many people for weight loss programs, some diet books and health advocates have been promoting low carb/high fat diets as a means of  improving insulin sensitvity.  And protecting people from developing diabetes.  In fact, improvement of insulin sensitivity is often listed as one of the reasons why the general public should follow low carb/high fat diets.

Crossfit Paleo Diet: Benefits of low-carb high-fat diets?

So far research has been inconclusive.  Some studies support the hypothesis that low carb/high fat diets help improve insulin sensitivity but others don’t.  Some have found that low carb/high fat diets make insulin sensitivity worse.  The study by Biehohuby et al. (2013) was undertaken to see how low carb/high fat diets change glucose and insulin handling.  Subjects were male rats.

Study Synopsis:

Four groups of rats were fed one of four different diets:

  • a low carb/high fat with normal amount of calories for a rat or
  • a low calorie low carb/high fat diet or
  • a high protein low carb/high fat diet, or
  • a low protein ketogenic low carb high/fat diet.

Sensitivity to glucose and insulin was tested.  Results were as follows:

  • Animals had lower fasting glucose and insulin levels (generally thought to be good)
  • the low carb/high fat diets impaired glucose tolerance (generally thought to be bad)
  • low carb/high fat diets impaired insulin sensitivity (generally thought to be bad)

Research Conclusions

Here are the scientists conclusion about their study in their own words:

“Taken together, these data show that lack of dietary carbohydrates leads to glucose intolerance and insulin resistance in rats despite causing a reduction in fasting glucose and insulin concentrations. Our results argue against a beneficial effect of LC-HF diets on glucose and insulin metabolism, at least under physiological conditions. Therefore, use of LC-HF diets for weight loss or other therapeutic purposes should be balanced against potentially harmful metabolic side effects.”

Many, if not most, people have heard or been told that a low carb diet is health protective. It may be a good strategy for weight loss.  Diabetics may also do well or better on a low carb diet.  However, it may not be good for otherwise healthy people to stay on low carb/high fat diets for long periods of time.

Many diet trends have roots in science and research. The Paleo diet is just one.  However, of these roots get tangled with dogma, loyalties, financial interests and personal reputations. It is not uncommon to hear disdain or contempt for people who do not follow low carb diets, as well as concern for the health of people who continue to eat carbohydrates.  At least among my crossfit paleo diet associates.  I As a scientist, I often wonder where dogmatic thinking comes from.  As a professor I wonder how best to teach people to use other approaches to figuring out the order of the universe.  Its not always easy.  It may be simply part of human nature to

  1. build little compartments
  2. stick things in the compartments
  3. put them back in the compartments if they get out
The WODMASTERS Rhino Design ruminates on Vitamin K

WODMASTERS Rhino thinks about low carb diets

The problem with taking this approach to health and nutrition information is that we are learning so much, so fast and more is pouring in every day.  Its awesomely incredible.  Really.  But with all these little bits floating around and new bits being added to the pile its hard to find permanent homes for everything.  A high fat diet may not belong in the “avoid” pile.  Maybe it should be taken out and placed into the “go for it” pile.  Better yet, keep it on the table and see what it fits into.

For Medical and Research People:

Might glucose challenge test results from people on low-carb/high fat diets lead to their classification as pre-diabetic?  What is the clinical significance of low-carb diet induced changes in glucose and insulin handling anyway?


Bielohuby M, Sisley S, Sandoval D, Herbach N, Zengin A, Fischereder M, Menhofer D, Stoehr BJ, Stemmer K, Wanke R, Tschöp MH, Seeley RJ, & Bidlingmaier M (2013). Impaired glucose tolerance in rats fed low-carbohydrate, high-fat diets. American journal of physiology. Endocrinology and metabolism, 305 (9) PMID: 23982154


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  1. Wow. Maybe this is me. Can’t get FBS below 100 no matter what. Maybe I should stop kicking myself.

  2. “However, it may not be good for otherwise healthy people to stay on low carb/high fat diets for long periods of time.”

    Agreed. I think this may be me. I have been so stressed bc my FBG have been over 100, sometimes even 125 and 113. I went into paleo with no health issues so I would consider myself ‘otherwise healthy’ person. I think it is time to adjust my macro to a bit lower fat and higher carb.

  3. I looked through the original article and it quickly dawned on me what is going on here. http://ajpendo.physiology.org/content/305/9/E1059.long The scientists state that the LC-HF diet induces lower blood glucose and insulin levels. However they then run “glucose and insulin intolerance” tests. Those tests involve intravenous infusions of glucose respectively up to a certain defined level. They then look at how the body deals with all of this glucose or insulin. In both cases they find a reduced processing capacity and so declare “glucose and insulin intolerance”! This is stupid, irrelevant highly misleading when taken out of context. The important thing is that blood glucose and insulin levels are lower – there is no tendency towards diabetes and no tendency towards practical insulin resistance. However the scientists use this perverse testing procedure to pronounce the exact opposite. For this to be true in real life it would have to in turn create raised overall blood glucose and/or insulin levels – and it doesn’t. After 4 weeks on the diets the LC-HF (with high fat -not protein) rats were 10% lower in body weight than all the other rats and had lower blood glucose and insulin levels. You didn’t report that.

    It’s pretty obvious that if you don’t use a muscle it shrinks – well that’s what’s happening to the pancreas when the carb load is removed from the body. Just like you cannot lift such a heavy weight as before when you stop using your muscles – flooding the body with intravenous glucose and insulin will obviously show up a reduced capacity to process them – in the short term. That’s not a bad thing – it’s a good thing – it just means we are now not adapted to eating carbs. The mistake being made by the scientists is the standard one. They are once again assuming that the default setting and priority is carb metabolism; It is NOT. Carbs are a non-essential macro-nutrient. The body clearly adjusts to optimal settings in their absence.

    For survival – this fits with their report. If you are starving and find some fruit you would want insulin resistance to be initially high so that any excess food is driven into your body fat storage system. Insulin resistance is a survival mechanism for the ice age and seasonal changes. In rodents it’s linked to hibernation cycles. Did the scientists even consider this? No.

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