How important is protein in a low-carb diet?

It has been known for decades that eating more protein can assist with weight loss, yet most people do not eat enough protein for general health let alone to help them with weight loss or muscle maintenance! This article looks at why we need protein in the diet; which foods to get it from; how much to consume; dispels myths about protein and bone loss or kidney damage and looks at whether protein supplements can help with weight loss.

Why we need protein in our diets

Proteins are molecules that come in an assortment of shapes and sizes made up of various combinations of the 20 amino acids, 9 of which are essential, meaning we must consume them in our diet because our body cannot make them. Proteins have many different roles in the body including:


· Provide structure to support tissues such as bones, skin, connective tissue, hair and muscles.

· Enable contraction of muscles.

· Make enzymes that speed up chemical reactions.

· Make antibodies that help fight infection.

· Make hormones that carry chemical messages.

· Transport of oxygen, cholesterol, and other molecules around the body.


So, you can see, protein is pretty important to health!


Main sources of protein – animal vs plant

Protein can come from both animal and plant sources. Animal sources include meat, fish, dairy and eggs, and plant sources include legumes, beans, soy (plus soy products such as tofu), nuts, seeds and quinoa. Animal sources are generally considered superior because they contain all 9 essential amino acids, are more digestible, and more bioavailable (absorbable) than plant proteins (1).


Plant proteins tend to be missing at least 1 essential amino acid, often more; and can be harder to digest and fully absorb due to the presence of fibre and other substances (2). This may make it more challenging for a vegetarian or vegan to lose weight using a low-carb approach, though it is possible. Sufficient essential amino acids can be obtained from a vegan diet by using food pairings (that pair legumes with grains or legumes with nuts or seeds) to ensure the entire range of amino acids is consumed with each meal.


Table 1 – protein content of various foods

How does protein help with weight loss?

Protein works in two main ways to assist in weight loss:


1. It suppresses appetite and reduces hunger (3). This is a well-studied phenomenon, which is related to the effects of amino acids on the brain (4) and possibly by inducing an improvement in leptin sensitivity (an appetite suppressant)(5). Appetite suppression is a major reason why low-carb diets can assist with weight loss with many people following this dietary pattern only eating one or two meals per day without feeling hungry.


2. It increases energy expenditure (6). This means it enables you to burn calories more quickly, mainly by increasing fat burning over the day, whilst sparing muscle loss (7). Also, maintaining a high protein diet after weight loss has been achieved helps to ensure a higher energy expenditure is maintained, irrespective of carbohydrate intake (8), enabling weight loss to be maintained (9)(10).

Can high protein diets cause bone loss and kidney problems?

It has been suggested in the past that consuming large amounts of protein may lead to health problems such as weakened bones and kidney damage. However, more recent research suggests that not only does a high protein diet not lead to these problems, it may actually improve bone strength (11) and improve kidney function in people with mild kidney disease (12).


How much protein should you eat on a low-carb diet to help with weight loss?

Your ideal intake of protein depends on your health, body composition, main weight goal, and the type, intensity, duration, and frequency of your physical activity. The UK government guidelines recommend consuming around 55g protein per day for men and 45g protein per day for women, which equates to about 0.75g per kg/body weight (13). This recommendation was made in 1991 and has not been updated since, but many nutrition scientists now consider this to be inadequate for most people’s needs as it only addresses the minimum amount of protein needed to prevent deficiency, rather than an optimum amount to maintain health.


It is now generally understood that overweight and obese people who want to lose fat mass, but preserve muscle, should aim for between 1.2-1.5g protein per kg/body weight. If you are very athletic or physically active and want to lose weight, then you should aim for 1.6-2.4 g protein per kg/body weight (14). Protein intake should be distributed fairly equally between each meal to preserve muscle function and prevent muscle loss, with each meal containing 25-30g protein (15). In the UK and US protein distribution tends to be skewed towards the evening meal with protein consumption at breakfast and lunch being too low to meet nutritional needs.


Use the table 2 below to calculate your daily protein requirements according to your current weight (or use this useful protein calculator) and remember to distribute it between all your meals!


Table 2 – Protein intake guide

What about protein powders?

Whey protein powder (derived from dairy) is a high-quality complete protein supplement. Several studies have shown that whey protein can help with a weight loss by reducing appetite (16), reducing waist circumference and improving cardiometabolic risk factors such as lowering cholesterol and reducing waist circumference (17), whilst also preserving muscle mass (18).


Soy protein supplements have also been shown to help with weight loss, particularly in Asian and non-menopausal women (19) but it is absorbed more slowly than whey protein and has very low levels of two crucial amino acids, methionine and lysine, making it less able to stimulate muscle growth (20). Soy protein supplements also have less impact on cardio-metabolic risk factors and don’t suppress ghrelin (the hunger hormone) as much as whey powders (21).


Both whey and soy powders can help to boost protein intake if you are struggling to meet your requirements through food alone, which may be the case for people following a vegetarian or vegan diet or in people who wish to reduce their meat consumption. Whey protein seems to be more effective overall, but soy protein supplements can be a useful addition for vegans.

Conclusion

Protein is an important part of our diet and most people, though eating government recommended amounts of protein, generally do not eat enough protein for optimal health. Protein intake is an important part of a weight loss programme as it reduces appetite and feelings of hunger, making it easier to reduce the amount of food eaten per day, whilst preserving muscle mass and increasing energy expenditure. High protein diets do not induce bone loss or cause kidney damage to people with healthy kidneys. Animal sources of protein are superior as they contain all 9 essential amino acids and are more absorbable and digestible, but with careful food pairing it is possible to meet protein requirements with plant-based foods as well. Whey or soy protein supplements may make a useful addition to those who find eating sufficient protein per day challenging.

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