eGFR stands for estimated glomerular filtration rate and it is an estimation of how well your kidneys are working. eGFR is calculated based on the creatinine levels in the blood. 
Glomerular filtration rate is a measure of how well your kidneys are functioning. Kidneys remove waste from the blood using tiny filters called glomeruli. GFR represents the amount of blood filtered every minute. However, GFR can be complicated to measure. Instead, estimated GFR (eGFR) is used and uses a calculation based on the amount of creatinine present in the blood in combination with your age, sex and ethnicity. Creatinine-based eGFR tests are accurate, but some research suggests that a combination of creatinine and cystatin C may be more precise in certain circumstances. 
Creatinine levels can vary in different individuals. For example, those with higher muscle mass will have increased creatinine levels which may lead to results which are outside of normal parameters. As well as this, creatinine levels will rise and eGFR levels will fall transiently after periods of intense exercise but will rapidly return to normal. 
eGFR is used to measure the function of the kidneys. If your eGFR is low it can be an indication of chronic kidney disease (CKD), symptoms of which may include:
Swollen ankles, feet or hands , 
Although eGFR is associated with increased kidney function decline, it is possible to see some improvement. If your levels are mildly low, it may be possible to see improvements by making some changes to your lifestyle.
Eating a healthy, balanced diet could contribute to an improvement in eGFR values. A study by Miyatake et al., (2011) found that eGFR could be improved through lifestyle changes including a reduction in abdominal circumference.  A greater waist to hip ratio can mean you are at greater risk of decreased filtration. You should keep your salt intake low – less than 6g per day. The Mediterranean diet is associated with a reduced risk of chronic kidney disease as well as other medical conditions. 
The Mediterranean diet is classified by a high intake of vegetables, fruit, legumes, nuts, cereals and olive oil, a low intake of dairy products, saturated fats, meat and poultry. Instead, the diet encourages a moderate intake of fish and has been linked to a reduced risk of mortality.
Exercise is an important factor in a healthy lifestyle. In general, most people should aim to carry out around 150 minutes of aerobic exercise every week. Exercises may include walking, jogging, swimming, cycling, team sports and tennis. However, you should spread the amount of exercise over a few days.
A study has shown that patients who have cardiovascular disease and chronic kidney disease could improve their renal function with exercise therapy. 
 Lab Tests Online UK. (2018). eGFR-Calc. Creatinine Clearance. Available at: https://labtestsonline.org.uk/tests/egfr-calc-creatinine-clearance
 Inker, L, A., Schmid, C, H and Tighiouart, H et al., (2012). Estimating Glomerular Filtration Rate from Serum Creatinine and Cystatin C. The New England Journal of Medicine: 367, pp 20-29.
 Poortmans, J, R and Ouchinsky, M. (2006). Glomerular Filtration Rate and Albumin Excretion After Maximal Exercise in Aging Sedentary and Active Men. The Journals of Gerontology: 61(11), pp 1181 – 1185.
 National Health Service. (2016). Chronic Kidney Disease. Available at: https://www.nhs.uk/conditions/kidney-disease/diagnosis/
 O’Hare, A, M. (2009). The Management of Elderly People with a Low eGFR: Moving Toward an Individualized Approach. American Journal of Kidney Disease: The Official Journal of the National Kidney Foundation: 53(6), pp 925-927.
 Weis, L., Metzger, M and Haymann, J, P et al., (2013). Renal Function Can Improve at Any Stage of Chronic Kidney Disease. PLOS One.
 Miyatake, N., Shikata, K., Makino, H and Numata, T. (2011). Decreasing Abdominal Circumference is Associated with Improving Estimated Glomerular Filtration Rate (eGFR) with Lifestyle Modification in Japanese Men: A Pilot Study. Acta Medica Okayama: 65(6), pp 363-367.
 Huang, X., Jiménez-Moleón and Lindholm, B et al., (2013). Mediterranean Diet, Kidney Function, and Mortality in Men with CKD. Clinical Journal of the American Society of Nephrology: 13(5).
 Toyama, K., Sugiyama, S and Oka, H et al., (2010). Exercise Therapy Correlates with Improving Renal Function Through Modifying Lipid Metabolism in Patients with Cardiovascular Disease and Chronic Kidney Disease. Journal of Cardiology: 56, pp 142-146.