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The Power of Protein In Your Diet!

>> Wednesday, March 2, 2016

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!

Follow me on twitter! @drsuepedersen © 2016


C Nelson, PhD RD March 17, 2016 at 11:50 AM  

Hi Dr Pedersen - I am interested in your comment that most people do not consume sufficient protein. Many of the provincial nutrition surveys done in the mid 90s to early 2000s showed that Canadians protein intake fell within the AMDRs ( which was confirmed by the 2004 Canadian Community Health Survey ( . The NHANES has reported similar data for Americans (

Any information you have showing the contrary would be of interest - thank-you

Dr. Sue Pedersen March 18, 2016 at 1:20 PM  

Dear Dr Nelson,

Thank you so much for your comment!

My comment that most of us do not get enough protein is in the context of weight management, as noted in the post: I have framed these points in the context of a person who is struggling with weight (as the majority of Canadian adults are).

While protein intake in Canadians may fall in the AMDR, several lines of research suggest that a more generous intake of protein is beneficial for weight maintenance and prevention of weight regain.

For example, it has been demonstrated that a protein intake of 18% compared with 15% resulted in better weight maintenance in overweight subjects after weight loss of 7.5%, with improved body composition, fat distribution, substrate oxidation, and satiety (Lejeune MP Br J Nutr 2005;93:281).

The present overall view is that a minimum of 0.7-0.8g/kg/day is of benefit for weight maintenance, and also for body composition and satiety in the context of weight loss. This is based on it benefits for sustained satiety, energy expenditure, and FFM, all of which are negatively impacted by diets that do not provide adequate protein.

If you look at a diet with the average of 16.5%E protein:

1500 kcal diet: 16%E = 240 kcal in protein / 4cal/g = 60g

if person weighs 70kg, this is 0.85g/kg/d

if person weighs 100kg, this is 0.6 g/kg/d

Now we could certainly have the discussion of whether this calculation should be based on ideal body weight, lean body weight, and how these numbers would differ for a lower or higher calorie intake diet. But the general principle applies that in particular for weight management, many individuals would benefit from a little more protein in their diet.

This topic is nicely reviewed in: Bray, G and Bouchard, C. 2014. Handbook of Obesity: Clinical Applications (Volume 2), chapter 15 p.193.

Dr. Sue


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