You’ve heard it before – you can’t grow stronger, more defined muscles without good nutrition. It’s nutrition that supplies the fuel and building blocks your muscles need to grow. You’re probably familiar with the “big three” macronutrients – protein, carbohydrates, and fat – but you may know less about the concept of nutrient partitioning and the role it plays in muscle growth. What is nutrient partitioning and how can it affect your body composition?
What is Nutrient Partitioning?
Nutrient partitioning is about where the energy from the nutrients you take in goes and whether the calories from those nutrients are burned as fuel, stored as fat, or taken up by muscle tissue to build new muscle. The degree to which each takes place depends on a variety of factors, including genetics and hormonal influences, particularly insulin.
After you eat a carbohydrate-rich meal, the carbs you ate are broken down into glucose. As glucose enters the bloodstream, your pancreas responds by releasing insulin. The discharge of insulin is a necessary step since insulin opens up the doorway of cells to let glucose come in. Without enough insulin, glucose stays in the bloodstream leading to an abnormal rise in blood sugar while your poor cells are starving for glucose but can’t get it due to lack of insulin. This is an example of very poor nutrient partitioning and what happens when a person has type 1 diabetes and doesn’t make enough insulin. So, you need a certain amount of insulin, but not too much, for healthy nutrient partitioning.
Another Example of Bad Partitioning
At the other end of the spectrum is insulin resistance where you have too much insulin floating around. People who are insulin resistant produce insulin, but their cells don’t respond to it. Their cells have lost the ability to recognize and respond to it. To fix matters and get glucose into cells, the pancreas goes into overdrive producing more and more insulin in hopes of pushing insulin into the unresponsive cells. Unfortunately, insulin is also a fat-storage hormone and when you have levels of circulating insulin, it makes it easy for your body to store glucose as fat – another form of nutrient partitioning that’s not ideal
If you exercise or do resistance training, you want a significant amount of nutrient partitioning into muscle tissue. Insulin is important here too. It helps get amino acids, the breakdown products of dietary protein, into cells. The more sensitive your muscle cells are to insulin, and the less insulin resistant, the easier it is to partition amino acids from the food you eat into muscle rather than fat. So, better insulin sensitivity leads to more favorable nutrient partitioning – into muscle tissue where you want it rather than into fat cells.
The Role Other Hormones Play
Other hormones also have an effect on nutrient partitioning, including testosterone and cortisol. Testosterone promotes partitioning of nutrients into muscle while the stress hormone cortisol has the opposite effect. When you have a high cortisol level, you get muscle breakdown and enhanced partitioning of nutrients into fat cells around your waist and abdomen – another kind of partitioning you don’t want.
How you sequester nutrients is also partially determined by genetics. Some people, because of good genetics, gain mostly muscle when they consume more calories, assuming they’re resistant training, while other less fortunate individuals partition a larger portion of those extra calories into fat. It works the other way too. People with good genetics, also lose less muscle when they diet and shed more body fat instead.
You can’t choose your genetics, but you can change how you partition nutrients and calories, to some degree, through diet and exercise.
The Role of Diet in Nutrient Partitioning
Now that you know that insulin plays a major role in how you partition nutrients and calories, the goal is to avoid eating a diet that promotes insulin resistance. That means avoiding refined carbohydrates and added sugar. Lean sources of protein, whole fruits and non-starchy vegetables (not fruit juice), and moderate amounts of fiber-rich whole grains and nuts help to stabilize insulin and prevent rapid fluctuations in blood sugar.
If you have insulin resistance, weight loss is more challenging, but losing even 10% of your body weight will increase insulin sensitivity and improve the way you partition nutrients. A good diet for insulin resistance and overall health is the Mediterranean diet, a diet rich in unprocessed foods, fruits, vegetables, whole grains, fish, and healthy fats from nuts and olive oil. Grab a copy of a Mediterranean cookbook and discover how diverse and satisfying a Mediterranean diet can be.
The Role of Exercise
All types of exercise, especially high-intensity exercise, increases insulin sensitivity and this improves how you partition nutrients. Another powerful way to change where your nutrients go, whether they go into fat or muscle, is weight training. The more lean muscle you have on your frame to suck up nutrients, the less likely you are to store what you eat as fat. Plus, research shows resistance training increases insulin sensitivity independent of changes in body composition. Plus, you get the benefit of increasing anabolic hormones like testosterone and growth hormone when you train using heavy resistance. These are hormones that work in your favor when you’re trying to improve your body composition.
The Bottom Line
A variety of factors, including hormones and genetics, influence where nutrients are diverted when you eat a meal. Wouldn’t it be nice if the macronutrients you ate went directly to muscle tissue and none ended up as jiggly fat on your tummy or waistline? Even people with the best nutrient partitioning genetics don’t have it that easy – but you can increase the degree to which you deliver nutrients to muscle as opposed to fat by changing your diet and by doing high-intensity exercise and resistance training. Lifestyle changes really do matter and you can overcome a lack of good calorie and nutrient partitioning genetics, so keep weight training and eating a clean diet.
Body Recomposition. “Calorie Partitioning: Part 1”
Medscape Multispecialty. “Insulin Sensitivity Improved with Mediterranean-Style Diet” December 12, 2012.
Med Sci Sports Exerc. 2006 Jul;38(7):1208-15.
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