A question I often get asked is – what is the best source of energy in our diet?

Well, when we talk about energy in our diet, we are talking about calories (calories = energy).   The four main calorie sources are protein, carbohydrates, fat, and alcohol.  A balance of protein, carbs, and fat is important.  Most people are a little (or sometimes a lot) low in protein content in their diet, and should be eating more.

Following are some interesting points about protein and metabolism.  I have framed these points in the context of a person who is struggling with weight (as the majority of Canadian adults are), and therefore, I am writing along the lines of keeping calorie intake down while ensuring a balanced diet.

Also please note I am not recommending the consumption of alcohol – I am including it here to be complete (and practical, as many people do have some alcohol in their diet).

1.  The number of calories (kcal) per gram of each source varies:

  • protein: 4 kcal/g
  • carbs: 4kcal/g
  • fat: 9 kcal/g
  • (alcohol: 7 kcal/g (this is pure alcohol; if you consider one ounce (28g) of a 40% alcohol such as vodka, then the calories are calculated as 28g x 7kcal/g x 40% = 78 calories))
So far, protein and carbs come out looking the best – ie lower calories per gram than fat (or alcohol). 

2.  Protein makes you feel fuller than carbs, which in turn make you feel fuller than fat.  And alcohol does not make you feel full at all.   It’s not completely clear exactly how protein makes us feel more full, but mechanisms may include increased glucose production (gluconeogenesis), and a decrease in ghrelin (the hunger hormone).
3.  The energy required to digest protein is highest (called the ‘thermic effect of food’):
  • protein: about 25% of the calories consumed are used to digest it
  • carbs: about 7%
  • fat: 1-2%
  • alcohol: 22%  (Hang on.  Don’t take this as a good thing.  When you consume alcohol, your body stops burning all other fuels (eg fat and carbs) to preferentially burn the alcohol. See here for more on this.)
4.  Protein intake helps to retain lean body mass (muscle), which gives you a higher basal metabolism compared to having less muscle and more fat.
5.  Protein also stimulates the burn of fat (called ‘fatty acid oxidation’).
So as you can see, there are a number of metabolic benefits to eating protein.
Next question: How much protein should we eat? Well, the acceptable range as per the American Food And Nutrition Board of the Institute of Medicine  is between 10-35% of total daily calorie intake for healthy adults.    A high protein diet is considered to be 25% or more of total calorie intake.

How do you convert these numbers into calories?  Well, for example, if your calorie needs are 2000 calories per day, and you are aiming to eat 20% of your daily calories as protein, then about (2000 x 20% =) 400 calories of your day would be protein.  Since protein is 4 calories per gram, this would equal about (400/4 = ) 100 grams of protein per day.
Is it possible to eat too much protein? While an upper limit of protein intake that could cause harm hasn’t been clearly identified, there are a few possible concerns:
  • Protein metabolism results in excretion of nitrogen based waste products in the urine, which could potentially cause damage in excess (science: by increasing glomerular pressure and hyperfiltration).  I have had kidney specialists tell me that for people with healthy kidneys, they recommend a maximum of 1.5 grams of protein per kilogram of ideal body weight per day (though this isn’t clearly supported by dietary clinical trials).I know. It’s getting complicated.

    *** For people with kidney problems, it is very important to talk to your doctor about how much protein is safe for you.***

  • The acid load of high protein diets can increase blood pressure.  Also, the excess acid load is buffered by bone, which may increase the draw of calcium from bone.

Bottom line: Most of us don’t eat enough protein, and trading up some carb in our diet for protein is a good idea (most of us are overeating carbs, which is why the tradeoff for most people should come from carbs).It’s pretty tough to overdo protein with natural food sources – but don’t go chugging volumes of protein shakes as this may overdo it.  Talk to your doctor or dietitian to ensure you are getting an appropriate balance of protein (vs carbs vs fat) in your diet.

As for what kind of protein we should be eating…. stay tuned!


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