Chronic Kidney Disease (CKD) is characterized by a gradual loss of kidney function. The kidneys play a vital role in filtering wastes and excess fluids from the blood, which are then removed in urine. In the early stages of CKD, individuals might experience few noticeable signs or symptoms, making early detection and management crucial.
The Interplay Between Kidney Disease and Body Weight
Maintaining a healthy weight is essential for individuals with kidney disease. It's not uncommon for those with CKD to be either overweight or underweight. While weight gain might prompt a doctor to suggest weight loss, kidney disease itself can sometimes lead to unintentional weight loss. In cases of IgA nephropathy (IgAN), fluid retention can cause weight gain, while kidney-related issues can result in fat loss in specific areas of the body. Monitoring these changes with a healthcare team is vital.
Kidney Disease and Obesity
Obesity, defined as a Body Mass Index (BMI) of 30 or higher, is associated with an increased risk of developing CKD and its progression to advanced stages. A healthy BMI score falls between 18.5 and 24.9, while a score of 25 to 29.9 indicates overweight. Obesity is linked to several risk factors for kidney disease, including type 2 diabetes, hypertension (high blood pressure), hyperlipidemia (high cholesterol), coronary heart disease, and sleep disorders. Diabetes and high blood pressure are the leading causes of kidney disease, accounting for up to two-thirds of all CKD cases.
Research suggests that weight gain may account for a significant portion of the risk of high blood pressure. Furthermore, individuals with higher body weights and CKD may experience a faster progression to kidney failure. In those with immunoglobulin A nephropathy, complications like high blood pressure, proteinuria (protein in the urine), and kidney lesions were more prevalent in those with higher body weights.
The Role of Intentional Weight Loss
Doctors may recommend weight loss to reduce the risk of serious health complications. Studies have shown that losing weight can lower the risk of developing type 2 diabetes, sleep apnea, high blood pressure, high cholesterol, and asthma.
Read also: Managing Stage 3 Kidney Disease with Diet
However, it remains uncertain whether weight loss can improve outcomes or kidney function for individuals with CKD. Some studies have found little or no differences in weight loss, proteinuria, or blood pressure between people with CKD who were trying to lose weight and those who weren't. More research is needed to determine if weight loss in people with CKD can help them live longer or prevent heart disease.
Dietary Considerations in Kidney Disease
If you're living with kidney disease, you may have to follow a special diet to help balance the levels of electrolytes, minerals, and fluid in your body.
Dietary restrictions for kidney disease can make losing weight more difficult. A high-protein diet has been proposed as a way to increase weight loss while still feeling full. However, if you’re following a low-protein diet to treat kidney disease, you may not be able to eat high-protein foods.
Examples of foods that may need to be limited if you have kidney disease include:
- High-sodium foods: Added table salt, packaged foods, and fast food
- Protein: Meat, beans, and nuts
- High-phosphorus foods: Deli meat, dairy products, oatmeal, beans, and soft drinks
- High-potassium foods: Oranges, bananas, potatoes, dairy products, and whole wheat bread
If you’re following a low-phosphorus or low-potassium diet, talk to your doctor and dietitian about which kidney-friendly foods you can add to your grocery list. Some examples of low-potassium vegetables include iceberg lettuce, cabbage, cucumbers, onions, and bell peppers. Low-potassium fruits include apples, berries, and pears.
Read also: Nutrition and stage 2 CKD
Unintentional Weight Loss in Kidney Disease
Although higher body weight is related to kidney disease, it’s also true that kidney disease can cause some people to lose weight. As cited in Current Opinion in Nephrology and Hypertension, you may have an increased risk of dying if you lose weight or body fat when you have kidney disease.
Kidney disease can cause you to lose weight if you don’t eat enough calories. As mentioned, a BMI of less than 18.5 is considered underweight.
If you have kidney failure, you may experience symptoms like nausea, vomiting, and loss of appetite that make it hard for you to eat enough food. If you’re on dialysis, your body may need more calories than you’re used to. Additionally, if you have a restricted diet, you may have to avoid some foods you enjoy eating. If you don’t get enough calories every day, you may start to gradually lose weight.
Some people with kidney failure can also develop wasting syndrome (called cachexia), which can cause the loss of fat and muscle. Wasting syndrome is caused by more than just a loss of appetite. In people with end-stage renal disease (ESRD), wasting syndrome can be caused by inflammation and differences in metabolism. Additionally, some appetite-suppressing hormones may build up in your body if your kidneys can’t effectively filter them out of your blood.
One of the unusual things that can happen in people living with the kidney disease called complement 3 glomerulopathy (C3G) is that some parts of the body might become unusually thin. This thinness can be in specific areas, like the muscles or fat tissue in certain parts of the body. Complement 3 is one of several proteins that team up in the body’s defense system, known as the complement system, to fight off infections. In C3G, the complement system can sometimes destroy fat cells under the skin, but it does this unevenly throughout the body. This process leads to some parts of the body appearing abnormally thin and others abnormally large.
Read also: Comprehensive Guide: Gastroparesis Diet
If you notice that you’re losing weight without trying, talk to your doctor right away. Your doctor or dietitian may be able to help you find ways to increase your daily calories.
Protein-Energy Wasting (PEW) and Cachexia in CKD
Wasting, also known as cachexia, is prevalent among patients with chronic kidney disease (CKD). It is important to distinguish wasting/cachexia from malnutrition, which results from insufficient food intake or an improper diet. Malnutrition is characterized by hunger, an adaptive response, whereas anorexia is prevalent in patients with wasting/cachexia. In malnutrition, energy expenditure decreases as a protective mechanism, while it remains inappropriately high in cachexia/wasting. Fat mass is preferentially lost in malnutrition, preserving lean body mass and muscle mass. Conversely, in cachexia/wasting, muscle is wasted, and fat is relatively underutilized. Restoring adequate food intake or altering the diet's composition reverses malnutrition, but nutritional supplementation does not entirely reverse cachexia/wasting.
The wasting/cachexia syndrome in CKD patients consists of anorexia, increased energy expenditure, decreased protein stores characterized by a low serum albumin, and loss of body weight and loss of muscle mass. Importantly, the individual components of this syndrome all represent risk factors for mortality in patients with CKD, which is significantly higher than the general population.
In the context of CKD, the term protein-energy wasting (PEW) has been proposed by The International Society of Renal Nutrition and Metabolism (ISRNM) to describe a “state of decreased body stores of protein and energy fuels (body protein and fat masses)”. The ISRNM suggested that the term cachexia be reserved for only the most severe forms of PEW. However, there is no obvious distinction between PEW and cachexia from a pathophysiology standpoint. Limiting the term cachexia to the extreme forms of PEW could be considered too restrictive.
Diagnostic Criteria for Cachexia/PEW
The diagnostic criteria for cachexia and PEW are similar, but not identical. Weight loss of at least 5% over 12 months or fewer, or a BMI < 20 kg/m2, is necessary for the diagnosis of cachexia; three of the following five additional criteria are also required: decreased muscle strength, fatigue, anorexia, low fat-free muscle mass, and abnormal biochemistry (including elevated inflammatory markers such as C-reactive protein (CRP) or interleukin (IL)-6, anemia [Hb < 12 g/dL] and hypoalbuminemia). The proposed criteria for a diagnosis of PEW fall into four distinct categories: (1) biochemical indicators, (2) low body weight, reduced body fat or weight loss, (3) decreased muscle mass, and (4) low protein or energy intake.
Biochemical Indicators of PEW
Among biochemical indicators of PEW, low serum albumin stands out as a consistent predictor of mortality in epidemiological studies of both adult and pediatric ESRD patients. A low serum albumin concentration is by far the strongest predictor of mortality and poor outcomes in adult ESRD patients on maintenance dialysis when compared to any other risk factors, including traditional and non-conventional ones.
Relatively low serum prealbumin is another indicator of PEW and a strong predictor of outcomes in maintenance dialysis patients. Changes in serum prealbumin over time are associated with corresponding changes in survival of ESRD patients. Dialysis patients with high serum prealbumin have lower proportion of body fat as well as higher proportion of muscle mass, which suggest that normal serum prealbumin is associated with reversal of the abnormal body composition in cachexia.
Other nutritional indicators that predict survival in maintenance dialysis patients include serum transferrin level and nutritional scoring systems such as the SGA and MIS which also correlate with quality of life. Low serum cholesterol has also been proposed as a biochemical indicator of PEW. Circulating inflammatory markers such as CRP, and proinflammatory cytokines such as IL-6 may also be persistently elevated in PEW but were not included as part of the criteria for diagnosis of PEW.
Causes and Manifestations of PEW in CKD
The pathophysiology of cachexia/PEW syndrome is CKD is multifactorial. Anorexia is caused by a combination of factors including altered taste. Although inadequate nutritional intake may contribute to wasting or cachexia, recent evidence indicates that other factors, including systemic inflammation, perturbations of appetite-controlling hormones from reduced renal clearance, aberrant neuropeptide signaling, insulin and insulin-like growth factor resistance, and metabolic acidosis, may be important in the pathogenesis of CKD-associated wasting.
Weight Change Patterns in CKD
Clinically significant weight change is common in moderate to severe chronic kidney disease but has no relationship to baseline kidney function. There is limited information published on the usual pattern of weight change in those with moderate to severe kidney disease and elevated BMI. Annualized weight changes are highly dependent on the follow‐up time, as small changes over a short period of time become relatively large changes if extrapolated over a year.
A study performed in an unselected group of patients with moderate to severe non‐dialysis CKD and overweight or obesity showed that a significant proportion experienced clinically significant weight changes, but because these changes were balanced, the mean weight for the group fell only modestly during follow‐up. There was no association between baseline severity of CKD and subsequent weight change.
The authors found a U‐shaped association between clinically significant weight change during the first year and death or the renal endpoint. This is because, in the absence of a deliberate attempt by the patient to gain or lose weight, the weight change likely represents a surrogate marker for other adverse changes in health and may not, itself, be on the causal chain for death. Successful, deliberate attempts to gain or lose weight appear to be rare in the CKD population.
Management and Lifestyle Recommendations
Maintaining a healthy weight is crucial for managing kidney disease and reducing the risk of complications. This involves a combination of dietary adjustments, regular exercise, and managing underlying medical conditions.
Lifestyle Recommendations for Stage 3a CKD
- If you smoke and/or use tobacco products, stop.
- Exercise regularly.
- Sleeping well is important, too.
- If you are overweight, losing weight through a balanced diet and physical activity can help improve your health in many ways.
- Find ways to reduce and manage stress in your life.
Dietary Recommendations for Stage 3a CKD
- If you have high blood pressure, it is important to limit your sodium (salt) intake to less than 2300 mg per day.
- Based on the results of your blood tests, your healthcare professional or kidney dietitian may also advise you to change how much potassium, phosphorus, and/or calcium you might be getting through your diet.
Medications
In stage 3a CKD, some of your medications may start to build up in your body. Ask your healthcare professional or pharmacist if any of your medication doses need to be lowered because of your stage 3a CKD.
Your healthcare professional may prescribe one or more medicines to help slow down or stop your CKD from getting worse. These medicines include an ACE inhibitor/ARB, an SGLT2 inhibitor and/or an nsMRA.
Other Ways to Lower Your Risk
People with stage 3a CKD should also avoid certain pain medicines known as non-steroid anti-inflammatory drugs (NSAIDs).
If your healthcare professional says you have metabolic acidosis, increasing the amount of fruits and vegetables you eat everyday can help lower the level of acid in your blood.
General Recommendations
- Follow instructions on over-the-counter medications.
- Maintain a healthy weight.
- Don't smoke.
- Manage your medical conditions with your doctor's help.