In this previous post, “Meet the Kitavans” we learned about the Pacific Island Kitavans, who had low levels of fasting insulin … and shockingly low fasting blood sugar levels.
The low levels of these two markers was EVEN MORE SHOCKING, because they reportedly ate a high carb diet, approximately 70% of their calories from carbs, mostly tubers and fruits.
I love reading studies on modern day hunter and gather tribes. Why? I want to see if we can determine the values of certain health markers … before modern living and modern foods became pervasive.
Today, we’ll meet the Kalahari Bushmen… another shocking paper, but for different reasons. As we’ll find out, the study isn’t as well designed as I’d like … but it’s results are very interesting!
Study: “Metabolic Responses to Oral Glucose in the Kalahari Bushmen”
I didn’t seek out another example of ‘primitive’ people who are apparently unaffected by modern society… this 1971 paper from the British Medical Journal found me.
The study reports the results of an Oral Glucose Tolerance Test given to Kalahari Bushmen.
Before we dig in to the study, for reference I want to share with you my Oral Glucose Tolerance Test experience, “Insulin Resistance Glucose Tolerance Test“.
My Oral Glucose Tolerance Test (OGTT)
I wrote an entire blog post on this test so I won’t go into a lot of details here but check out the post for more information.
An OGTT tests how well your body processes dietary glucose. The Kalahari were ONLY given 50 grams of glucose, with my OGTT, I took 75 grams of glucose.
Below is the guidance for blood sugars at the 2 hour mark back in 2012 when I performed my OGTTs with 75g of glucose.
below 140 mg/dl meant you had normal glucose tolerance
140 mg/dl to 199 mg/dl meant you were impaired
above 200 mg/dl meant you were diabetic
My Fully Fat Adapted OGTT Results (75g)
60 min - After One Hour Blood Sugar = 236
120 min - After Two Hours Blood Sugar = 182
* To adapt to glucose I consumed 150 grams of carbohydrates for 3 consecutive days before taking the OGTT again.
My 2nd OGTT Results - Glucose Adapted (75g)
60 min - After One Hour Blood Sugar = 209
120 min - After Two Hours Blood Sugar = 101
My blood sugars were much better after adapting to glucose (the 2nd OGTT) and were, according to the metrics provided, my glucose tolerance was in the normal range.
Now let’s look at the Kalahari…
The Kalahari Bushmen’s Oral Glucose Test
To sum up the study, researchers gave 50 grams of glucose to the 15 adult Kalahari Tribesmen, and measured their glucose, insulin and growth hormone levels. The results were compared to 10 non-obese ‘white controls’.
From the Summary, the Kalahari:
”showed relative glucose intolerance and significantly impaired insulin secretion.”
This is interesting! At this point my interest was piqued, as this was the COMPLETE opposite of the Pacific Island Kitavans.
Next up from the Introduction:
“They live by hunting game and collecting wild vegetation ("veldkos"), certain species of which seem to have high nutritive value (Wehmeyer et al., 1969), though their dietary habits are such that periods of semistarvation give way to episodes of overindulgence (Bronte Stewart et al., 1960).”
Periods of semistarvation and overindulgence … that sounds a lot like ‘feasting and fasting’.
Ok, we also know they are Hunter and Gatherers, who ate wild game and ‘veldkos’, which can be leaves, tubers, fruits, etc … this doesn’t tell us much about their macronutrient ratios.
Subjects and Methods
The plan was to give the Kalahari and the control group a 50 gram glucose dose and then test their blood samples for glucose, insulin and growth hormone levels.
An OGTT is typically done in the morning after fasting overnight but this was not done with the Kalahari, because…
“ an overnight fast would probably have been broken (owing to the almost continuous eating pattern of the Bushmen when food is available)”
So the researchers administered the tests to both groups in the afternoon, 4 hours after each group had eaten.
Blood samples were then taken at 60 and 120 minutes.
The Surprising Results
“Mean glucose levels were higher in the Bushmen at all stages, with significant differences at 0 and 120 minutes.”
Again, this is the complete opposite results found in the study comparing the glucose and insulin levels of the Kitavans with the Swedes!
Here’s a table of the results.
I’ll type out the results in case this is difficult to read.
Bushmen’s Glucose & Insulin:
Glucose at the start of the test = 95 mg/dl (mmol/l) and insulin 10 u/ml
Glucose at the 60 min mark = 160 mg/dl (mmol/l) and insulin 33 u/ml
Glucose at the 120 min mark = 121 mg/dl (mmol/l) and insulin 20 u/ml
Just want to point out, that I took a 75 g glucose load, and after being ‘glucose adapted’ had readings at 211 mg/dl (1 hr) and 101 mg/dl (2hr). The Kalahari Bushmen only had a 50g dose of glucose.
“Mean glucose levels were higher in the Bushmen at all stages, with significant differences at 0 and 120 minutes.”
The statement above was made when comparing the Bushmen with the ‘white control group’.
And then this…
“…their mean two-hour post-glucose level of 121 mg/ 100 ml could be regarded as falling within the "diabetic" range.”
Wow! Kalahari Bushmen, falling within diabetic range of glucose tolerance… that is shocking to me. Given my own OGTT experience, I wondered if the Kalahari were ‘fat adapted’? (See below)
“…the Bushmen, in fact, consumed fairly large amounts of carbohydrate-rich vegetable food during the week before testing;“
So… based on the information above, we would have to assume the Kalahari were ‘glucose’ adapted…. and based on the blood glucose levels at the 120 min mark, the Kalahari were insulin resistant.
Kalahari Insulin Resistant?
The Kalahari insulin levels were ONLY after a four hour fast and not ‘overnight fasting’ as the Kitavans were.
I was hoping to be able to compare the Kalahari with the Kitavans, but we wouldn’t be comparing apples to apples.
The Kalahari’s fasting insulin level of “10 u/ml” was a surprise, the Kitavans were in the 3.4 to 3.9 range. Still, when compared with the ‘white control group’ who were tested under similar conditions, the Kalahari’s blood glucose was still higher at each testing interval.
But are the Kalahari Insulin Resistant? Here’s their HOMA-IR results, a test for insulin resistance. Calculation = Glucose X Insulin / 405
Note: Above 1.0 is insulin resistant (bad), below 1 is insulin sensitive (good).
Kalahari Homa-IR score = 2.23 (NOT GOOD)
White Control Group Homa-IR score = 3.14 (REALLY NOT GOOD)
To answer the question… yes, based on the Kalahari’s HOMA-IR score they are insulin resistant. How much of this was caused by the lack of a ‘true’ overnight fasting number?? Probably some. Their glucose and insulin levels could have been lower given another 4-5 hours of fasting.
However, even given the limitations of this study, and there are several … the Kalahari Bushmen were less insulin resistant than the “white control group” and that’s not a surprise.
In Closing
I enjoy reading studies of modern day hunter and gatherer tribes, primarily so I can attempt to glean information about what human health markers might have been before modern civilization and the diseases of modern living.
This 1971 study raises more questions than it answers but I will attempt to see if their apparent insulin resistance caused health problems years later.
Until next time, thanks for reading and may you all obtain and maintain … truly normal blood sugars!