Madeleine Hull
A protein-restricted diet is a diet in which people reduce their protein intake. It is used as a therapy for inherited metabolic disorders, such as phenylketonuria and homocystinuria, and can also be used to treat kidney or liver disease. The amount of protein considered low varies depending on the individual's health condition and needs. For example, the Kidney Disease Quality Outcomes Initiative (KDOQI) guidelines recommend a protein intake of 0.55–0.60 g of protein per kilogram of body weight for adults with CKD stages 3–5. While a protein-restricted diet has been shown to have benefits, such as improving metabolic health and longevity in rodent models, it is important to note that the applicability of these findings to humans is still uncertain.
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What You'll Learn
Protein restriction and CKD
Protein is an essential part of our diet, used to build muscle, heal, fight infection, and stay healthy. However, for those with kidney disease, a low-protein diet is often recommended. This is because, in kidney disease, the kidneys struggle to remove all the waste from the protein in the diet, which can cause nausea, loss of appetite, weakness, and changes in taste.
The exact amount of protein in a restricted diet will depend on the individual's body size, nutritional status, and the specifics of their kidney problem. A low-protein diet (LPD) is typically defined as 0.55–0.60 g of dietary protein per kilogram of body weight, while a very low protein intake is 0.28–0.43 g/kg. However, some guidelines recommend less restriction, with a normal protein intake of 0.8–1 g/kg per day.
The effectiveness of protein restriction in slowing the progression of kidney disease is somewhat unclear. While some studies have shown benefits, particularly in those with diabetes or chronic glomerular diseases, others have found little to no difference between low-protein and normal-protein diets. Additionally, there are concerns that a low-protein diet could lead to malnutrition, and that the restrictions could negatively impact patients' quality of life by forcing them to change their cultural norms and dietary habits.
For those with CKD who are on dialysis, a higher amount of protein in the diet is necessary to maintain blood protein levels and improve health. Dialysis removes protein waste from the blood, so a low-protein diet is no longer needed. It is important to consult with a healthcare professional or dietitian to determine the appropriate amount and type of protein for an individual's specific needs.
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Protein-restricted diets and metabolic health
Protein-restricted diets have been a topic of interest for their potential to improve metabolic health and slow ageing. While protein-rich diets are perceived to support muscle mass retention and enhance longevity, emerging evidence presents a paradox. Moderate protein consumption contributes to health maintenance, but excessive intake is associated with an elevated risk of chronic diseases, notably obesity and diabetes.
Several clinical and rodent studies have demonstrated the benefits of low-protein diets on metabolic health and longevity. In one study, mice were given one of twenty-five different macronutrient diets, and the longest lifespan was associated with diets low in protein and high in carbohydrates. Another study showed that a low-protein and high-carbohydrate diet provides similar benefits to calorie restriction in terms of insulin, glucose, lipid, and HOMA levels, despite increased energy intake. However, the mechanism behind these effects remains unknown, and it is unclear if these findings apply to humans.
In adults, dietary protein is effective for muscle health. A randomised controlled trial found that a high-protein diet combined with exercise improved muscle power and functional physical performance in middle-aged obese adults. In the elderly, higher protein intake is required for muscle health. The existing evidence supporting the benefits of protein-restricted diets on metabolism comes from studies on young and middle-aged subjects, not the elderly.
Dietary protein restriction has been studied in patients with metabolic syndrome, a cluster of conditions including obesity, insulin resistance, dyslipidemia, and hypertension. A randomised controlled trial found that a 50% reduction in protein intake for 27 days promoted weight loss and reduced blood glucose, lipid levels, and blood pressure. Another study found that both a caloric restriction diet and an isocaloric protein restriction diet resulted in weight loss in individuals with metabolic syndrome.
While protein restriction has shown potential benefits for metabolic health in certain contexts, it is important to note that dietary protein restriction for patients with cirrhosis has led to malnutrition. Therefore, it is crucial to carefully consider the specific circumstances and needs of individuals when discussing dietary protein restriction.
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Protein-restricted diets and food sources
Protein-restricted diets are often recommended to help treat certain health conditions. For instance, dietary protein restriction is helpful in controlling hyperphosphatemia and metabolic acidosis. It is also necessary for those with genetic disorders that affect protein metabolism, such as homocystinuria and phenylketonuria. Protein-restricted diets are also associated with lowered cancer incidence and a reduced risk of mortality from cancers in humans. In patients with CKD, dietary protein restriction can reduce proteinuria and act synergistically with antiproteinuric agents.
However, protein restriction has its downsides. Dietary protein restriction, which has an imperfect evidence base, will likely have a much smaller benefit when added to foundational therapies for CKD. A large controlled trial in Italy that included 456 patients with a variety of renal diseases showed that a low-protein diet produced only a small, statistically insignificant benefit at 2 years. A low-protein diet is not advisable unless you have an underlying health condition and are under direct medical supervision. Protein deficiency can cause impaired immune function, muscle loss and decreased growth.
Protein-restricted diets are usually focused on the low-protein components of meals, such as grains, vegetables, or fruits. Some examples of grains are rice, oats, bread, pasta, and barley. Vegetables include tomatoes, asparagus, peppers, broccoli, and leafy greens. Fruits can be apples, bananas, pears, peaches, berries, and grapefruit. You can still include meat and plant-based proteins in your diet, but only in small amounts.
Protein can be obtained from both plant and animal sources. Animal sources of protein, such as meat, eggs, and milk, as well as soy and quinoa, are called complete proteins, meaning they contain all the essential amino acids the body needs and are the highest-quality protein sources. Essential amino acids can also be obtained from plant-based foods, but most plant-based proteins are incomplete, meaning they do not contain all the essential amino acids.
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Protein-restricted diets and weight loss
A protein-restricted diet involves limiting the consumption of high-protein foods and focusing on eating fruits, vegetables, and healthy fats. It is typically recommended for individuals with kidney-related disorders, such as kidney disease, to prevent the buildup of urea in the blood, which can cause fatigue and loss of appetite.
Protein-restricted diets have been a subject of interest in metabolic health research. Studies in rodents have shown that low-protein diets can lead to weight loss and improved metabolic health. For example, mice fed low-isoleucine diets were leaner and exhibited healthier blood sugar metabolism. Similarly, a study on 25 different diets assigned to mice for 19 months revealed that diets low in protein and high in carbohydrates were associated with longer lifespans.
In humans, the impact of protein-restricted diets on weight loss is less clear. While some studies suggest that low-protein diets can aid in weight loss by reprogramming metabolism, the full effects of Branch Chain Amino Acid (BCAA) restriction in humans are not yet fully understood. Additionally, long-term, controlled diet studies that can be conducted in rodents are more challenging to perform in human subjects.
It is important to note that protein-restricted diets may not be suitable for everyone. Older adults, for example, may require additional protein due to muscle wastage associated with aging. Furthermore, a poorly planned low-protein diet can lead to nutritional deficiencies and health issues, including muscle loss and impaired immune function. Therefore, individuals considering a low-protein diet should consult a doctor or dietitian to ensure it is safe and appropriate for their needs.
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Protein-restricted diets and kidney health
Protein-restricted diets have been a topic of interest for scientists and dietitians for their potential to slow the progression of chronic kidney disease (CKD). While protein is essential for building muscle, healing, and fighting infection, excessive protein intake has been associated with an elevated risk of chronic diseases, including obesity and diabetes.
High protein intake can lead to increased intraglomerular pressure and glomerular hyperfiltration, causing damage to the glomerular structure and potentially resulting in or aggravating CKD. A low-protein diet (LPD) of 0.6–0.8 g/kg/day is often recommended for individuals with CKD to help manage the disease and reduce the risk of end-stage kidney disease (ESKD) and death. However, the effectiveness of LPDs in retarding CKD progression has been inconclusive, with some studies showing only small benefits or no significant difference compared to normal protein diets.
Several clinical and rodent studies have demonstrated the potential benefits of LPDs on metabolic health and longevity. These studies suggest that reducing the ratio of protein intake to macronutrients can improve metabolic parameters and extend lifespan. However, the applicability of these findings to humans remains uncertain, and more research is needed to fully understand the underlying mechanisms.
While protein restriction can be beneficial in certain cases, it is important to note that malnutrition is a concern, especially in patients with advanced liver disease or cirrhosis. Proper monitoring by a physician and skilled dietitian is crucial to ensure the safety and acceptance of protein restriction regimens. Additionally, individual preferences, cultural norms, and patient education play a significant role in the successful adherence to LPDs.
In summary, protein-restricted diets have shown potential in slowing the progression of CKD and improving kidney health. However, the effectiveness of LPDs is still under investigation, and personalized approaches that consider an individual's body size, nutritional status, and kidney problem are essential to determine the appropriate amount and type of protein in the diet.
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Frequently asked questions
A protein-restricted diet is one in which people reduce their protein intake. The amount of protein considered "low" varies depending on the individual's health condition and needs.
A protein-restricted diet has been shown to improve metabolic health and longevity in rodent models. It also helps control hyperphosphatemia and metabolic acidosis. In people with diabetes, it can help modify the glomerular filtration rate, filtration fraction, and fractional clearance of albumin, which may positively impact the progression of diabetic renal disease.
A protein-restricted diet is recommended for people with inherited metabolic disorders such as phenylketonuria and homocystinuria. It can also be beneficial for people with kidney or liver disease. However, it is important to consult a physician and a skilled dietitian before starting any dietary restrictions to ensure it is done safely and acceptably.
Some people may find it challenging to adhere to a protein-restricted diet as it may require a significant change in cultural norms and dietary habits. Additionally, there is a concern that a very low-protein diet may lead to malnutrition, especially in people with advanced liver disease.
