As per title.
“The good thing about science is that it’s true whether or not you believe in it.” Neil deGrasse Tyson.
Tampilkan postingan dengan label Good Science. Tampilkan semua postingan
Tampilkan postingan dengan label Good Science. Tampilkan semua postingan
The Science Behind the Paleolithic Diet.
Hat-tip to Melissa McEwen for posting the above-titled video on Facebook. It's 27 minutes of common sense from Matt Lalonde Ph.D Harvard University Chemistry and Chemical Biology.
Good Science: Doubly-labeled water
I was reading an interview with Rudolph L. Leibel and doubly-labeled water was mentioned. This sort of stuff fascinates me. Using doubly-labeled water, a mass spectrometer, loads of measurements and some mathematics, it's possible to work out how many kcals someone is burning. This method costs an arm & a leg. So, how does doubly-labeled water work?
Chemistry 101:
Water has the formula H2O. H stands for Hydrogen and O stands for Oxygen.
Elements have isotopes. Hydrogen has two isotopes, Deuterium and Tritium. Deuterium oxide, or D2O is known as heavy water and one use for heavy water is the manufacture of atomic bombs, if you recall the film "The heroes of Telemark". Deuterium is non-radioactive, as is heavy water. Tritium is radioactive.
Oxygen has three stable non-radioactive isotopes one of which is O-18. This can be used to make labeled water H2O-18. Mix D2O with a bit of H2O-18 and you have doubly-labeled water. Now what? To quote Leibel:-
"The interesting thing is that when you give somebody water like this, the deuterium comes out of the body which is determined by water turnover in the individual. The O-18 is in equilibrium with carbon dioxide, so the O-18 comes out by two mechanisms: first with normal water by transpiration, perspiration and urine, but also in the breath.
The difference between those two decay curves (the O-18 comes out faster), which we obtain by getting urine from these patients every day for 10 days-that gap is proportional to carbon dioxide production in that individual. By doing this, we can figure out how much carbon dioxide this person made over a period of 10 days. Knowing that, and knowing what the so-called diet quotient is - in other words, what the ratio of carbohydrates to fat in their diet is - you can back-calculate the amount of oxygen used to produce that amount of carbon dioxide.
So by some simple algebra using the rate of carbon dioxide excretion, you can actually calculate how much oxygen their body used in the process of oxidative metabolism. That is a very critical number because it tells you how much energy they burned. Oxygen consumption can be immediately converted into calories.
So we measure caloric expenditure both by figuring out how many calories it takes to make their body weight absolutely stable, and checking that number by also using this double-doped water excretion technique using mass spectroscopy. It's quite expensive: the isotopes to do such a study cost about $500, not including the spectroscopy."
See A comparative study of different means of assessing long-term energy expenditure in humans.
Ain't science wonderful?
Chemistry 101:
Water has the formula H2O. H stands for Hydrogen and O stands for Oxygen.
Elements have isotopes. Hydrogen has two isotopes, Deuterium and Tritium. Deuterium oxide, or D2O is known as heavy water and one use for heavy water is the manufacture of atomic bombs, if you recall the film "The heroes of Telemark". Deuterium is non-radioactive, as is heavy water. Tritium is radioactive.
Oxygen has three stable non-radioactive isotopes one of which is O-18. This can be used to make labeled water H2O-18. Mix D2O with a bit of H2O-18 and you have doubly-labeled water. Now what? To quote Leibel:-
"The interesting thing is that when you give somebody water like this, the deuterium comes out of the body which is determined by water turnover in the individual. The O-18 is in equilibrium with carbon dioxide, so the O-18 comes out by two mechanisms: first with normal water by transpiration, perspiration and urine, but also in the breath.
The difference between those two decay curves (the O-18 comes out faster), which we obtain by getting urine from these patients every day for 10 days-that gap is proportional to carbon dioxide production in that individual. By doing this, we can figure out how much carbon dioxide this person made over a period of 10 days. Knowing that, and knowing what the so-called diet quotient is - in other words, what the ratio of carbohydrates to fat in their diet is - you can back-calculate the amount of oxygen used to produce that amount of carbon dioxide.
So by some simple algebra using the rate of carbon dioxide excretion, you can actually calculate how much oxygen their body used in the process of oxidative metabolism. That is a very critical number because it tells you how much energy they burned. Oxygen consumption can be immediately converted into calories.
So we measure caloric expenditure both by figuring out how many calories it takes to make their body weight absolutely stable, and checking that number by also using this double-doped water excretion technique using mass spectroscopy. It's quite expensive: the isotopes to do such a study cost about $500, not including the spectroscopy."
See A comparative study of different means of assessing long-term energy expenditure in humans.
Ain't science wonderful?
When good science goes bad
I was rummaging through PubMed (as you do) and it occurred to me that there's a problem.
1) The conclusions in the abstracts don't always tie-up with the data in the full studies.
2) There is no mention of who funded the studies.
3) There is no mention of any conflict of interest for the authors.
Some abstracts link to a free full study and some don't. This makes it difficult to know which studies have been "fixed" to achieve a desired outcome by tweaking the methodology. For example, here are some studies involving Hunter SJ, in chronological order:-
Elderly women in northern New England exhibit seasonal changes in bone mineral density and calciotropic hormones which is about seasonal variations in Vitamin D status affecting bone density and was co-authored by Michael Holick.
Demonstration of Glycated Insulin in Human Diabetic Plasma and Decreased Biological Activity Assessed by Euglycemic-Hyperinsulinemic Clamp Technique in Humans which is about how high blood glucose glycates insulin before it's even secreted, resulting in it working less well in muscle cells.
Reduced prevalence of limited joint mobility in type 1 diabetes in a U.K. clinic population over a 20-year period which pretty much does what it says on the tin.
Then, Hunter starts working for The Sugar Bureau and begins co-authoring studies like this:-
Effect of eucaloric high- and low-sucrose diets with identical macronutrient profile on insulin resistance and vascular risk: a randomized controlled trial, scrutinised in Who pays the piper
Low-fat versus low-carbohydrate weight reduction diets: effects on weight loss, insulin resistance, and cardiovascular risk: a randomized control trial, scrutinised in Who pays the piper part 2
and
Session 4: CVD, diabetes and cancer Diet, insulin resistance and diabetes: the right (pro)portions, which concludes "based on the results of diabetes prevention trials focusing on lifestyle measures, evidence favours low-fat diets as the preferred approach for weight loss and diabetes prevention."
Evidence favours low-fat diets for weight loss and diabetes prevention, huh? See Low-carb diet pitted against low-fat PLUS medication (low-carb still wins) and Diabetes Update
So, getting paid by an organisation which promotes the consumption of sugar makes good science go bad.
1) The conclusions in the abstracts don't always tie-up with the data in the full studies.
2) There is no mention of who funded the studies.
3) There is no mention of any conflict of interest for the authors.
Some abstracts link to a free full study and some don't. This makes it difficult to know which studies have been "fixed" to achieve a desired outcome by tweaking the methodology. For example, here are some studies involving Hunter SJ, in chronological order:-
Elderly women in northern New England exhibit seasonal changes in bone mineral density and calciotropic hormones which is about seasonal variations in Vitamin D status affecting bone density and was co-authored by Michael Holick.
Demonstration of Glycated Insulin in Human Diabetic Plasma and Decreased Biological Activity Assessed by Euglycemic-Hyperinsulinemic Clamp Technique in Humans which is about how high blood glucose glycates insulin before it's even secreted, resulting in it working less well in muscle cells.
Reduced prevalence of limited joint mobility in type 1 diabetes in a U.K. clinic population over a 20-year period which pretty much does what it says on the tin.
Then, Hunter starts working for The Sugar Bureau and begins co-authoring studies like this:-
Effect of eucaloric high- and low-sucrose diets with identical macronutrient profile on insulin resistance and vascular risk: a randomized controlled trial, scrutinised in Who pays the piper
Low-fat versus low-carbohydrate weight reduction diets: effects on weight loss, insulin resistance, and cardiovascular risk: a randomized control trial, scrutinised in Who pays the piper part 2
and
Session 4: CVD, diabetes and cancer Diet, insulin resistance and diabetes: the right (pro)portions, which concludes "based on the results of diabetes prevention trials focusing on lifestyle measures, evidence favours low-fat diets as the preferred approach for weight loss and diabetes prevention."
Evidence favours low-fat diets for weight loss and diabetes prevention, huh? See Low-carb diet pitted against low-fat PLUS medication (low-carb still wins) and Diabetes Update
So, getting paid by an organisation which promotes the consumption of sugar makes good science go bad.