Dietary protein, serum albumin and health
When was the last time you thought about your serum albumin? You might have glanced at it the last time you got a lab panel at your doctor’s office, and as long as it was within the normal lab limits, you probably didn’t give it much thought. You should look at it a little more closely the next time you get a lab done because your serum albumin is a pretty good barometer of your overall health.
Albumin is the most abundant protein in blood plasma.
(Let’s take a brief digression to define a few terms so that we’re all on the same page. Blood is blood. Blood is what you get if you cut yourself. When you get your blood drawn, that dark red stuff is the blood, which includes the red blood cells, white blood cells, and other cellular components. Plasma is what’s left over when all the cells are removed. Typically, when blood is drawn it is put into a tube, and the tube is put into a centrifuge. The whirring of the centrifuge drives all the cells to the bottom of the tube; the yellowish fluid left on top is the plasma. If you put the whole blood in a tube and let it sit, the blood clots into a big glob and drops to the bottom, the clear yellowish fluid left on top is the serum. Basically serum is plasma that has had all the clotting factors removed. For our discussion of albumin, it doesn’t really matter. Albumin is measured in the serum, and so is called serum albumin. But it is the most abundant protein in the blood other than the proteins making up all the cells.)
A number of health and lifestyle factors influence albumin levels. Malnutrition, especially protein malnutrition, liver and kidney disease, smoking, a decreased muscle mass, a loss of strength, and low levels of physical activity are all associated with lower albumin levels. More importantly, albumin is a determiner of how sick you are and how likely you are to die should you be admitted to the hospital with a severe illness. The lower your serum albumin, the greater your chances of succumbing. It’s a lab value that doctors working in intensive care units monitor very carefully.
It has generally been accepted that serum albumin falls with increasing age, which makes sense if you think about it. As you get older your muscle mass decreases, your liver and kidneys don’t work as well, and you’re not as strong: in short, you’ve got all the conditions that go along with a decreasing serum albumin. If you get sick enough to require the services of an intensive care unit, your lower albumin that goes along with your increased age marks you as less likely to survive the experience than a younger person with a higher albumin.
That has been the conventional wisdom at least. But some new research sheds light on a phenomenon that MD and I noticed in our practice: increased dietary protein intake promotes the synthesis of more albumin and raises albumin levels in the blood, even in older people.
Before we get into the specifics of the research, I want to digress once more and discuss a little about what albumin does. It doesn’t just sit there, riding along in the blood. It has a number of vital functions. Albumin attaches to and transports hormones, including thyroid hormone throughout the body. It carries free fatty acids to the liver; it transports bilirubin. Albumin also transports drugs, binds with calcium, and helps maintain the blood acidity in a narrow range. It’s most important function is that it maintains osmotic pressure, which keeps the plasma inside the blood vessels where it belongs instead of allowing it to ooze out into the tissues. How does it do this? What is osmotic pressure?
Let’s make another digression to flesh out the idea of osmotic pressure, which is one of the most important forces acting in the human body.
Imagine that you have a small aquarium. This aquarium is half full of regular old tap water. Across the middle of the aquarium you stretch a thin membrane from side to side like a tennis net. The membrane is attached on both sides and the bottom and the top. And the membrane allows water to freely flow through it, but it doesn’t allow anything else to flow through other than the water.
Now you’ve got your aquarium half full of water with a membrane dividing one side from the other. The water level is the same on both sides of the membrane. If you pour some water into one side of the aquarium, the water level in that side will rise as compared to the level on the other side of the membrane. But as water seeps through the membrane, in pretty short order the water level will be once again the same on both sides.
Let’s say that now we drop a few tablespoons of salt into the water on one side of the membrane. Remember, only water can cross the membrane, not salt. What’s going to happen? Water, as we all know, seeks its own level and will ultimately stay at the same level across the permeable membrane, i.e., there will not be a higher level on one side than the other once it equilibrates. What drives the equilibration is the pressure difference between on side and the other. When you pour the plain water in one side, the pressure rises on that side, the increased pressure drives the water through the membrane until the pressure is equal on both sides.
The same phenomenon exists with concentrations of water, and here’s where it starts to get interesting. If you mix salty water with non-salty water in the same container, the water will mix together until the concentration settles out somewhere in the middle. But if you make the water more salty on one side of the membrane stretched across the aquarium, what happens? The water can go back and forth, but the salt can’t. What ends up happening is that in an attempt to equalize the concentration of salt, the non-salty water crosses the membrane to try to dilute the salty side. As the non-salty water crosses the membrane, the level of water gets higher on the salty side. The increased water pressure then tries to drive the water back to the side with the lower level and less pressure. As you let the system come to equilibrium, the water on the salty side rises to a certain level increasing the pressure of that level. That increased water pressure becomes equal to the forces driving the water to try to equalize the concentration of salt. That pressure is called osmotic pressure.
If you pour more salt in the salty side, the level of the water rises a little bit more as compared to that on the non-salty side because you have increased the osmotic pressure.
Albumin is the substance that provides the osmotic pressure in our blood in the same way that the salt did in our aquarium experiment.
The albumin attracts the fluid in the blood and keeps it in the blood vessels. Blood vessels are porous, and without the osmotic pressure of the albumin will let the fluid part of the blood escape our into the tissues.
We’ve all seen this phenomenon in pictures of starving children. These kids don’t get enough protein, they can’t make albumin, with little albumin their blood vessels can’t retain the fluid part of the blood. It seeps out into their tissues and makes the big bellies we associate with starving kids. Their bellies are full of the fluid that should be in their blood vessels. If they are given protein to eat, their livers begin to make albumin, the albumin exerts its osmotic pressure and draws this fluid from the tissues back into the blood, and the large, protuberant bellies go away.
As you can see, albumin is extremely important, and it serves us well to make plenty of it.
The most recent edition (July 2007) of the Journal of Nutrition published a terrific study of the synthesis of albumin as a function of both protein intake and age.
Subjects of both sexes and of two age groups ( 21-43 y and 63-79 y) were given varying amounts of dietary protein after which their rates of albumin synthesis were measured. The amounts of protein were set at 125%, 94% and 63% of the recommended dietary allowance (RDA). (The RDA for protein is 0.8 gm/kg body weight/day.) 125% of RDA comes out to be 1 gm of protein per kg (2.2 lbs) body weight per day, so a person weighing 70 kg (154 lbs) got 70 gm protein, which isn’t a huge amount.
The protein in the study came from all food sources including grains, dairy, fruits and vegetables. No meat was served because – as the authors pointed out – the protein content was too high. They wanted to be able to carefully provide a precise amount of protein while keeping the calories at a substantial level. A low intake of calories inhibits the synthesis of albumin, and since they wanted to measure albumin synthesis as a function of protein intake, they gave the subjects plenty of calories. Had they used meat, they would have exceeded the protein limits they were studying.
After data analysis it turned out that male subjects made a little more albumin than female subjects across the age ranges, which goes along with the slightly higher ‘normal’ levels for males as compared to females. The most important findings were that as dietary protein increased, so did the synthesis of albumin and that these changes held across the ages of the subjects. In other words, older people who consumed as much protein as younger people made the same amount of albumin as younger people.
All this is important because it is important for elderly people to maintain their albumin levels for optimal functioning and resistance to disease. Elderly people are the very people who are the most afraid of heart disease and who get most of their information via the mainstream media. These are the people who have bought into the notion that cholesterol is dangerous, despite the mountains of data showing that – like with albumin – elderly people do better with higher cholesterol levels. The elderly are the ones who fall prey to the statin and low-fat diet pushers. As a consequence, the elderly seldom get even the RDA of protein, which the above study shows is less than adequate. And since the elderly don’t get enough protein, they can’t make the albumin they need.
For those of you (us? I just had a birthday) who are elderly, eat meat, increase your protein intake. If you don’t want to eat meat, at least drink a protein shake with a fair amount of leucine in it every day. For those of you (us?) who aren’t elderly, make sure you get plenty of protein. It’s good for you. It will increase your albumin levels, build muscle mass, and even increase your thermogenesis. And it makes you less hungry. Go for it.