High Protein Diet Side Effects

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Posted by Linda O'Byrne (Atkins Nutritionist)

High protein diets are becoming increasingly popular, but there are a number of potential side effects you should be wary of. Find out more.

There’s no doubt that protein is needed in the body and there’s a common misconception that Atkins is a high protein diet, when it’s not. On Atkins, we recommend moderate protein intake with a higher proportion of energy from dietary fat and lots of vegetables; which provide complex carbohydrates.

There has been ongoing debate about the side effects of high protein diets and whether they are a safe for weight loss. Conventionally, the side effects of high protein diets have centred on possible side effects from long term use.


This have been fairly inconclusive but point to potentialities like constipation from lacking fibre intake, however this can easily be avoided by including high-fibre vegetables in your diet.


Another media scare is that a high protein diet ‘could’ increase your intake of fat which ‘could’ contribute potentially to heart disease. However, research that has been emerging over the last few years has shown that it’s only when combining high fat with high carb that this risk may be of concern. Remember on Atkins, protein isn’t eaten in excess and fat is burnt as energy.

Osteoporosis and high protein diets

The conjecture is that high protein diets, based around meat, can lead to greater bone density loss among women by aged 65 while women who don’t eat meat have lower bone density loss. 

This is based on high protein diets requiring more calcium to be processed and excreted which may come from the bones if unavailable elsewhere. However, calcium is created by eating other products such as dairy.

On the flip side, there is also research that low protein diets can have a similar affect by reducing intestinal calcium absorption so it remains inconclusive if this is a demonstrable side effect.

High protein diets and renal problems

As the kidneys filter proteins, it’s claimed a high protein diet can put an additional strain upon the kidneys. However, this advice tends only to be directed at people with existing renal function issues. Studies of bodybuilders with high protein diets have therefore often been used to show a lack of impaired renal function among the healthy.


High protein diets and diabetes

The problem with this theory is that it’s acknowledged that dietary restriction alone cannot cause this to occur. Additionally, many studies have indicated the reverse that less carbohydrates and more proteins can maintain a better glucose homeostasis.

High protein diets and cancer

The latest alleged side-effect came to light early this year with two scientific studies purporting to show how high protein diets could be as bad as smoking.

One study focused on mice and one study focused on humans, and it was the latter which garnered the most column inches with the claims that cancer rates among human aged 50-65 may be related to high protein intake by the production of insulin like growth factor IGF-1. 

Curiously, the converse was said to occur among people aged over 65. It’s still early days for either of these studies to approach anything conclusive as fact, with so far it being the conviction of one scientist in particular with no more than a possible association being mooted. 

The diet used in this study had no bearing on Atkins and the macronutrient intakes were very different from what we recommend at Atkins.

High protein and weight loss

Too much protein certainly isn’t recommended for weight loss as it can be converted to glucose, by way of ‘gluconeogenesis’. This is one reason we recommend 115-175g (in weight) of protein per meal, or up to 225g if you’re a bigger man. Any more than this may hamper your results.