This article suggests that the reason the Tsimane people of Bolivia experienced a significant, well-documented drop in their body temperature and metabolic rate over the past 15 years is that their fat became less saturated due to newly available “store bought foods”, most of which are loaded with polyunsaturated fat (PUFA). This drop in body temperatures mirrors what has happened globally as vegetable oil consumption has increased worldwide.
If you’ve been following along with The ROS Theory of Obesity and The SCD1 Theory of obesity Part 1 and especially Part 2, you will know my theory that increasing the saturation level of fat entering the mitochondria – both from stored body fat and from diet – increases your metabolic rate. This happens because saturated fat causes Reactive Oxygen Species (ROS) to be produced in the mitochondria. ROS is a signal to the nucleus that the body is burning fat and that energy levels are high. The ROS lead to an increase in thermogenesis, which means literally “making heat”. Thermogenesis literally burns off calories as heat.
I am speculating, of course. I don’t know the types or quantities of store bought foods that are being consumed by them. The potential mechanism by which vegetable oil could reduce metabolic rate is well known, however.
Human Body Temperatures are Dropping!
Several interesting papers came out in 2020 around the issue of declining body temperature. The first pointed out that the body temperature of Americans has been decreasing since the industrial revolution.1
An even more interesting one showed a decline of body temperatures by 0.5 degree C (0.9 degree F) in an Amazonian population that was well documented and happened between 2004 and now.2 Here is a graph from that paper of the average body temperatures of men and women at different ages with samples taken between 2002-2004, 2007-2012 and 2013-2018. I think the Female temperatures are particularly compelling.
From 2002-2006, female body temperatures were right at 37.0 for the entire human lifespan. By the 2007-2012 time period, young women had a small drop in average body temperature and older women had a significant drop. By 2013-2018 the body temperature of women of all ages had collapsed to a new average of 36.6 degrees. This is an interesting number, because the first paper states “Recently, an analysis of more than 35,000 British patients with almost 250,000 temperature measurements, found mean oral temperature to be 36.6°C”. So the Bolivian “Forager-farmers” now have the same body temperature as modern Britons.
The drop in temperature was accompanied by a drop in metabolic rate. Unfortunately, metabolic rates did not begin being measured until 2012, when they were in steep decline before plateauing in 2014.
The hypothesis of both of these papers is that infections cause increased body temperatures – as you know if you’ve ever had the flu – and the reason that body temperatures have declined over time is that humans have eliminated many sources of infections including parasites. Ultimately, though, the Bolivian paper concludes, “Despite the possibility that changing infection rates and reduced morbidity can explain some of the temporal decline in body temperature, several lines of evidence suggest that these changes alone are insufficient. … These observations suggest that factors other than inflammation and immune activation are likely to influence body temperature.”
The paper, however, gives little indication as to the diet of the Bolivians or how it might have changed. But this pop-science article about the paper gives a little insight, “The Tsimane people live in villages without running water or electricity, and subsist largely on rice, plantains and the starchy root vegetable manioc. Rapid community changes over the last few decades include increased access to store-bought foods and antibiotics.”
So the Tsimane had a very high starch diet to which, during the time period that their body temperatures were dropping, they added “store-bought foods”. As you probably know, store bought foods are a fantastic source of vegetable oil. I would suspect that vegetable oil itself would be in demand for adding to starches.
Does Vegetable Oil Lower Body Temperature?
Luckily, this paper also came out in 2020.3 This is a mouse study. Look at how much the body temperature of mice whose diets are supplemented with margarine plunge when subjected to three hours of cold compared to their starch eating counterparts. Sorry about my arrow drawing skills.
The same paper showed that mice fed margarine had a buildup of linoleic acid (PUFA) in their tissues. Compared to mice fed butter, they had lower body temperatures and produced less UCP1 (more on that below) in the fat cells. They failed to do thermogenesis in response to cold!
As I’ve said before, the mitochondria is like a battery. When fuel (fat or carbohydrate) is being burned, the Electron Transport chain pumps protons across the inner membrane, causing a voltage gradient. The outside of the membrane has a positive charge and the inside has a negative charge. It’s exactly like the positive and negative terminals of a battery.
The mitochondria uses this voltage gradient to do work. Typically, as the protons flow back through the membrane, through Complex 5 of the electron transport chain, the energy released is used to turn ADP into ATP. What the body is doing in all of this is converting one type of stored chemical energy (the hydrocarbon bonds in fat) into another type of stored chemical energy (ATP), that can then be used to do work – move a muscle.
UCP1 is an alternate route for protons to flow back through the mitochondrial membrane. Normally, a battery would be used to do work, just like in the mitochondria. For instance, a battery can turn on a light bulb. The light bulb is doing work – providing light. The light bulb provides “resistance” to electrical flow to do this work. Because of the “resistance” the electrons move slowly from one terminal to the other and a flashlight can turn on a bulb for quite some time.
What happens, though, if you just connect one terminal of the battery to the other without any resistance? The electrons can flow through RAPIDLY and give off a tremendous amount of heat. Very quickly, the voltage difference between the positive and negative terminals of the battery can be dropped this way. Soon, the battery will be discharged and no longer capable of performing work and a large amount of heat will be given off. Some people do this for fun:
So each UCP1 protein that is produced is like a tiny filament short circuiting the mitochondrial “battery”. It allows protons to flow back through, releasing energy from fat as pure heat, rather than storing it in another chemical form. When this happens, one magically burns off excess calories, body temperature rises and the voltage gradient across the mitochondrial membrane drops.
The margarine fed mice fail to produce UCP1 and fail to do thermogenesis.
What About The Starch Eating Humans?
I’m a huge fan of the study known colloquially as “The China Health Study”4, despite disagreeing with the conclusions of the authors about almost everything. The raw data they’ve collected is great and the original manuscript is fun to flip through to get ideas. You can pick up a copy at Amazon for only 500 bucks. One conclusion of the authors I DO agree with is this (emphasis mine), “ In the China Study, the least active Chinese consumed 30% more calories than their American counterparts yet their body weight was 20% lower. The excess calories were lost as heat rather than being stored as fat.”
So starch eating Chinese are very good at doing thermogenesis.
If highly saturated fat entering the mitochondria is what allows for thermogenesis, why then do the starch eating mice and starch eating humans have high metabolic rates and body temperatures?
The answer comes down to body fat saturation levels. The truth is that the body fat of starch eating creatures is highly saturated. I’ve seen this first hand in pigs and this is the whole basis of my Firebrand Meats Low-PUFA pork.
In the SCD1 Theory of obesity part 2 I highlighted a Tweet from Nathan Owens where he posted his results of a blood test showing the fat composition of his red blood cell membranes. The “China Health Study” reports the fatty acid composition of red blood cell phosphatidylcholine, which is to say membrane fats. That is also what is being reported in the test from Nate. Nate is a lean American, who eats a keto/mostly carnivore diet. Look at how unsaturated the body fat of a lean American eating lots of beef is compared to that of a Chinese person eating mostly starch!
|Nathan||Chinese Mean||American Range||Chinese Range|
|Omega 6 PUFA||30%||27%||26-45%||20-36%|
|Omega 3 PUFA||9.7%||3.3%||0.7-11.5%|
As you can see, there is ZERO overlap between the saturated fat levels of Americans and Chinese. All of the Chinese sampled had MUCH more saturated fat than Nate did and Nate is at the very high end of the American range. According to the company, the Americans with the most saturated fat have way less than the Chinese with the least.
Why is this? The body fat of people who eat mostly starch comes from DNL (De Novo Lipogenesis), which is only able to produce saturated fat, some of which gets converted to monounsaturated fat via the action of SCD1, which starch eating people don’t make too much of. Starch consumption from birth, if your mother and grandmother were also starch consumers, gives you very saturated fat! Saturated fat gives you ROS. ROS gives you the ability to produce UCP1 in your beige fat cells and burn off extra calories via thermogenesis.
It is well documented that the average body temperature and metabolic rate of the Tsimane people dropped over the last 15 years as they added “store bought food” to a diet of rice, plantain and manioc. Proposed reasons for this drop are reduced levels of infections, which is not supported by the evidence. I am proposing that polyunsaturated fat from the store bought foods were the key factor leading to the drop in body temperature.
I propose that the levels of PUFA from the store bought foods built up over the years in their fat cells, resulting in a steady decline in mitochondrially produced ROS, leading to a drop of production of uncoupling proteins and a reduction in thermogenesis.
In the fat comparison between American’s and Chinese I’m using red blood cell membrane composition as a stand in for stored fats. The composition will be different – membranes need to be very fluid and so they are very high in unsaturated fats and PUFA. Stored fats are much more saturated. But blood cell fats are easy to test and stored fat requires a biopsy. My opinion is that they will be tightly correlated: those with highly saturated membrane fats will have highly saturated storage fats.
I’ve had some questions about what is actually being tested in this test – membrane fats or whole blood. I talked to the company this morning and they told me that they separate out the phospholipids (membrane fats) from the other fats (stored for energy purposes) from the blood samples. They also said that the test will represent ALL phospholipids in whole blood – red blood cell membranes as well as the outer layer of LDL cholesterol particles (for instance). Finally they said that red blood cell membranes are the easy majority of the phospholipids, so that in their opinion the test is pretty accurate as to the composition of red blood cell membranes.
- 1.Protsiv M, Ley C, Lankester J, Hastie T, Parsonnet J. Decreasing human body temperature in the United States since the Industrial Revolution. eLife. Published online January 7, 2020. doi:10.7554/elife.49555
- 2.Gurven M, Kraft TS, Alami S, et al. Rapidly declining body temperature in a tropical human population. Sci Adv. Published online October 2020:eabc6599. doi:10.1126/sciadv.abc6599
- 4.Campbell TC. The China Study. The China Study. https://nutritionstudies.org/the-china-study/