Thursday, August 22, 2013

No Pump + Insulin Resistant? Maybe It's Your Healthy Low Salt Diet. Low Sodium Induced Increase in Aldosterone Has Direct Negative Impact on GLUT4 Mediated Glucose Uptake

A single Triple Whopper or about six whole steaks, what do you chose to get >75% of the 2g/sodium per day the feds are telling you you should maximally consume on a daily basis?
Today I felt kind of bored with covering only the latest studies. So I dug up one from 1999 that deals with the effects of dietary salt restriction on endothelial vasodilation (increased blood flow in the arteries) and insulin sensitivity by Ross D. Feldman and Nancy D. Schmidt. Yeah, the study is 14 years old, but when you've read today's SuppVersity article you'll probably still have learned something new - at least about "common wisdom".

If you also listen to the SuppVersity Science Round-Up on the Super Human Radio Network, you should be aware that very different rules apply with respect to salt consumption for athletes and physical culturists on a whole foods diet and the average sedentary inhabitant of the Western obesity belt (check out past episodes of the Science Round-Up).
Suggested Read: On "Clean Eating" being a myth - "A Tale of Macro- & Micro-Nutrient Modifi-cations" | read more
Talking about the ScienceRound-Up: In today's installment Carl and I will be talking about the latest meta-analysis on dairy and diabetes risk and how it's possible that only low fat dairy reduces the risk of diabetes. We will discuss how this relates to the differences in the fatty acid composition of milk which in turn depend on the feed the animals receive and whether there is in fact so much estrogen in milk that it can delay menopause. From there we will segue right into a discussion of the latest study on statins showing that they make you fat and diabetic and tell you which of the statins does what. If all works well, we will close the show by addressing Sarah M. Davis' question about a recently published and heavily discussed article that's titled "Why 'Clean Eating' is a Myth" (read it). I mean, is it really? Turn in live! at 12PM EST
What some of you may yet still not have on their radar is the fat that the "common wisdom" about salt being the root cause of all evil does not even apply to the majority of those guys and girls of whom you would expect they may in fact see benefits from a reduced salt consumption.

"Salt is bad, no matter what!"

In fact, Feldman & Schmidt were able to show that the provision of either normal or salt reduced diets to subjects aged 25 to 40 year.
Figure 1: Increased aldosterone levels during salt restriction will not only make you retain salt, but also reduce glucose uptake (Luther. 2011; my edits)
"Subjects were given a standardized diet that contained 75 mmol/L sodium chloride, 60 mmol/L potassium, and 20 mmol/L calcium for 14 days. Diets contained 16% protein, 54% carbohydrate, and 35% fat. Caloric intake was 2800 kcal/day. Subjects were advised to drink approximately 2L of water/day.

To assess the effects of dietary salt restriction independent of other dietary changes, subjects were randomized on a double blind cross-over basis to a daily supplement of 16 tablets of slow release sodium (Novartis, Mississauga, Ontario; 10 mmol/L sodium chloride/tablet) or matching placebo. Each were administered for 7 days." (Feldmann. 1999)
All of the participants had normal blood glucose levels, and were free of other abnormalities on history and physical examination. They did not smoke and their blood pressures levels ranged from normotensive to high normal/borderline. So, what would happen to the poor wretches consuming the additional sodium chloride tablets? Common wisdom tells us, their blood pressure will increase and they will develop metabolic abnormalities. Truth is (I quote from the study; Feldmann. 1999, my emphases), almost the exact opposite happened:
  • Did you know? Aldosterone increases are caused by falling blood pressure, increased potassium levels, a higher blood acidity and decreased sodium concentrations in the blood trigger, decreases occur when your blood pressure drops, the potassium levels get low and/or the sodium levels are high.
    Dietary sodium restriction was associated with a significant decrease in 24-h urinary sodium excretion. However, blood pressure (based on the average 24-h automatic ambulatory measurements) was not significantly decreased with dietary salt restriction.
  • Moderate salt restriction was associated with a significant increase in plasma norepinephrine concentrations. Dietary salt restriction was associated with a significant decrease in the glucose-to-insulin ratio, suggesting increased systemic insulin resistance. This decrease was primarily accounted for by an increase in plasma insulin concentration.
At the same time the researchers observed a significantly reduced effect of the vasculature to the insulin-mediated increase in blood flow, of which Hornstra et al. have shown only recently that it correlates negatively with blood pressure in overweight, but insulin sensitive individuals and may be the reason why those people don't suffer from the usual obesity related increases in blood pressure as well as its cardiovascular and renal consequences (Hornstra . 2013).

Most of you will remember the recent post about the ability of salt to block the negative effects of high intensity exercise on the cellular integrity of your heart and kidneys don't you?
Bottom line: If you are working out and sweating, even if it's not like a pig, SALT is the last thing to fear. In fact you can even increase your heart disease risk due to the negative impact on blood lipids (+10% total +12% LDL cholesterol in salt-sensitive and unsensitive normotensive subjects; Ruppert. 1991).

Now it is important to point out that it is not clear whether these effects are transient and a response to the abrupt changes in dietary salt in take that are characteristic of these short term intervention studies.

I am certainly not recommending you copy the salt intake of the average junk-food fanatic!

But let's be realistic, here: How much salt do you actually consume on a daily basis if you follow my advice and leave as much of the processed pre-packaged junk as you can right in the supermarket!? This will leave you with actually having to put salt on your foods and there really is no good reason for the average physical culturist not to so in a way that it's tasty and supplies you with one of the most important minerals in your body.

Suggest figure: Only obese people have increased risk of CVD with increasing sodium consumption | check it out the SuppVersity Facebook Wall

Reference:
  • Egan BM, Lackland DT. Biochemical and metabolic effects of very-low-salt diets. Am J Med Sci. 2000 Oct;320(4):233-9. Review.
  • Hornstra JM, Serné EH, Eringa EC, Wijnker MC, de Boer MP, Yudkin JS, Smulders YM. Insulin's microvascular vasodilatory effects are inversely related to peripheral vascular resistance in overweight, but insulin-sensitive subjects. Obesity (Silver Spring). 2013 Mar 20.
  • Luther JM, Brown NJ. The renin-angiotensin-aldosterone system and glucose homeostasis. Trends Pharmacol Sci. 2011 Dec;32(12):734-9.
  • Ruppert M, Diehl J, Kolloch R, Overlack A, Kraft K, Göbel B, Hittel N, Stumpe KO. Short-term dietary sodium restriction increases serum lipids and insulin in salt-sensitive and salt-resistant normotensive adults. Klin Wochenschr. 1991;69 Suppl 25:51-7.