Protein and carbs – get the balance right
Do high-protein, low-carb diets aid weight loss or are there issues to consider before you start cutting the carbs? Our nutritionist takes a look at the latest evidence.
Often viewed with suspicion, high-protein diets are thought, by some, to be just another fad. However, numerous high-protein eating plans claim cutting carbs in favour of protein not only helps you lose weight, but do so more effectively. Add to this that, as we age, there is an increasing need for high-quality protein to maintain muscle mass and it’s clear this is not a straightforward topic.
Discover more about popular diets including the macro diet, the keto diet and learn more about high-protein diets.
Do I need carbs?
We need to include carbs in the diet because they provide the body with glucose, which fuels our muscles and organs, including our brain. In fact, carbs are the body’s main source of energy. They’re broken down by the digestive system into glucose (sugar) before being absorbed into the bloodstream, from where the glucose can be used as ready energy or diverted to the muscles or liver for storage.
Often overlooked but an important type of carbohydrate, fibre is vital for general health as it may help reduce the risk of some diseases including bowel cancer, heart disease and type 2 diabetes. It also helps to promote digestive health and may help manage appetite.
The amount of carbs you need will depend on your age, sex, gender and activity levels. As a guide, the Reference Intake (RI), which is based on a moderately active adult female, is currently 260g of carbs per day. Although there is no RI for fibre, most experts agree that we should be consuming 30g daily.
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Do I need protein?
Protein is essential for growth, brain development, healthy bones, to regulate our hormones, support our immune systems and much more. In the UK, the Reference Intake (RI) is 0.75 gram/kg of body weight – this represents the minimum amount of protein you need to stay well and is based on an average, sedentary adult. This is a baseline, so to determine how much you need you will need to consider other factors such as your age, weight, gender, activity levels and your life stage.
For more information, read our expert guide on how much protein you need.
How does this compare to the popular keto diet?
Those following a keto diet tend to restrict their intake beyond guideline amounts with carbs typically restricted to no more than 20-50g per day, this is so that the body triggers a process called ketosis (this produces ketones that are used as an alternative energy source). To put this in perspective, an average banana contains 20g and a medium baked potato 41g, so clearly a strict keto diet demands careful planning and compliance. A set amount of protein is also suggested – the reason being that the building blocks of protein, known as amino acids, can be converted to glucose. The amount of protein suggested typically represents 10-20% of your daily energy intake and is determined so as to preserve lean body mass, including muscle, whilst not disrupting ketosis. In effect, the standard keto diet is a high-fat, low-carb, moderate protein diet.
Do carbs and protein work together?
Carbs, protein and fat form the three macronutrients – nutrients that we require in large amounts – and as such form the foundation of a healthy, balanced diet.
In addition to this, those who are active and especially those competing in endurance sports, require adequate carbs to optimise their performance and protein to support muscle repair and recovery.
Can a diet high in protein help me lose weight?
If your goal is to lose weight, it's useful to know a few facts. Fats and carbohydrates are considered our main fuels, which means we don’t typically use protein as a source of energy but we can do if we are not getting enough calories from other sources. Using protein for energy can give you a slight calorie-burning edge, that’s because protein has a greater ‘thermic effect’ than either carbs or fat – what this means is when we digest and absorb protein our body uses more energy. Adequate amounts of protein in the diet also promotes our sense of fullness from a meal, helping to regulate our appetite and limit snacking.
A number of studies suggest a diet higher in protein may help you lose body fat as opposed to lean muscle, which is always the aim if you're looking to lose weight. Furthermore, a higher protein intake appears to help manage the symptoms of metabolic syndrome, such as poor blood sugar control and insulin management as well as high cholesterol and triglycerides.
Are there better times of the day to eat protein or carbs?
Ideally, include some protein with each meal but focus especially on the morning – eating protein early in the day helps manage cravings and trains your circadian rhythm, and therefore may support better sleep.
Carbs are the body’s preferred energy source so if you plan to be active make sure you’ve eaten sufficient fuel in the form of carbs beforehand. The ideal sources include fibre-rich, complex carbs, like oats, as well as starchy vegetables including potatoes. Often considered a fattening food, potatoes provide resistant starch, a possible appetite suppressant. If your activity levels drop as your day progresses, you may wish to reduce the proportion of carbs on your plate.
Are there health implications to consider?
As with most diets, it is important to achieve balance. A prolonged intake of high amounts of protein at the expense of carbs has been associated with bone loss and potential kidney damage in those with existing renal issues; however, in otherwise healthy individuals, there is little evidence to this effect. In fact, in the otherwise healthy (including the elderly), a higher protein intake combined with minimal change in carbs, may help prevent the loss of muscle mass and strength and may help regulate appetite and blood sugar control.
The composition of your diet is of course important. For example, some high-protein diets restrict carbs so severely that they may lead to nutritional inadequacies and possibly a lack of fibre. Low-fibre diets are likely to impact the health of your gut and potentially increase the risk of colonic disease.
What does a healthy portion look like?
Protein and carbs both play a part in helping you shed excess weight and reach your optimal body composition. When choosing protein, it's worth remembering that animal and plant-based proteins are equally effective so opt for lean protein such as chicken, turkey, fish and dairy, as well as soy-based protein, beans, nuts and seeds – a healthy portion is about the size of the palm of your hand.
The type of carbs you choose is equally as important. Complex carbs, such as wholegrain bread, oats and rice, as well as fruit and veg are nutrient-dense and fibre-rich – a portion is about the size of your clenched fist.
Last words
In conclusion, striking the right balance between protein and carbs really depends on your age, gender, size and activity levels. For the majority of healthy adults, a diet higher in protein for a specified period (such as a few months), shouldn't cause a problem. That said, the implications of following a high-protein diet over a long-term period, combined with a restriction of carbs, is still being researched and may vary, dependent on age and genetics.
Don’t forget that UK RIs for carbs and protein are guideline amounts and your specific daily requirements will depend on your age, state of health, level of activity and stage of life, with mid-life and older people typically requiring more protein.
If you have a chronic health condition such as liver or kidney disease or diabetes, or if you are pregnant or planning a pregnancy, consult your GP before making any significant changes to your diet.
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This page was reviewed on 9 January 2023 by Kerry Torrens.
Kerry Torrens BSc. (Hons) PgCert MBANT is a BANT Registered Nutritionist® with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.
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