Researchers investigate impact of low-salt diets and ketogenic diet

Researchers have developed a novel test that identifies individuals who are the most likely to experience negative health effects if they eat a high salt diet. This new test and a second study showing that the ketogenic diet improves diabetes symptoms were presented today at the 71^st AACC Annual Scientific Meeting & Clinical Lab Expo, and could empower people to transform their health through dietary changes.

In recent years, numerous contradictory dietary guidelines have come out, leaving the public confused about what is truly healthy to eat. The American Heart Association recommends an ideal upper salt intake limit of 1.5 g/day for adults in order to prevent high blood pressure and cardiovascular disease. However, in 2013, the Institute of Medicine came out against cutting sodium levels below 2.3 g/day. So which organization is correct? The answer turns out to depend on an individual's genetically determined salt sensitivity. 14% of Americans are salt sensitive, which means that too much salt increases their risk of cardiovascular disease. Another 11% of Americans, however, are inverse salt sensitive and paradoxically develop high blood pressure with too little salt intake.

In the past, the only way to determine salt sensitivity was by placing a patient on a stringent, 2-week long salt-restricted diet. A faster, more convenient test has been developed by a team of researchers led by Kwabena Sarpong, PhD, of the University of Virginia School of Medicine in Charlottesville. This new test determines salt sensitivity by measuring a patient's dopamine 1 receptor (D₁R) recruitment, which plays a key role in telling the kidneys to excrete salt.

To validate this test, Sarpong's team used controlled changes in dietary salt to identify one group of salt sensitive individuals and a second control group of salt resistant individuals whose blood pressure does not fluctuate significantly in response to changes in sodium intake. From participants' urine, the researchers then isolated kidney cells known as renal proximal tubule cells (RPTCs). Sarpong's team exposed the RPTCs to salt and observed how much D₁R the cells mobilized in response. Salt sensitive individuals had the least D₁R recruitment, salt resistant individuals had moderate D₁R recruitment, and inverse salt sensitive individuals had high D₁R recruitment.

"If you know that you are salt sensitive, you can control this condition through lifestyle modifications or therapeutic interventions," said Sarpong. "But if you don't know your salt sensitivity index, you could potentially reduce your lifespan by as much as 20 years. There will therefore be profound benefits that come from understanding salt sensitivity and developing robust tools for diagnosing it."

The ketogenic (keto) diet is another health trend on which experts' views differ. Developed nearly 100 years ago to treat drug-resistant epilepsy, this extremely low carbohydrate diet has risen in popularity due to its reputation for speeding up weight loss. Experts caution that very little evidence indicates that the keto diet is effective over the long term for anything except managing epilepsy but some research does suggest that this diet could help with other medical conditions such as diabetes.

Researchers from CARE Hospitals in Visakhapatnam, India, have shown that the keto diet reduces blood sugar in type 2 diabetes patients, which supports the latter theory. Led by Kanchana Lakshmi Prasanna Angati, MD, the researchers recruited 115 Indian type 2 diabetes patients to follow the keto diet for 3 months. At the start of the study, participants' mean blood glucose and hemoglobin A1c (HbA1c) levels- both of which reflect blood sugar levels-;were 169 mg/dL and 7.8%, respectively. By the end of the study, mean blood glucose and HbA1c levels had dropped for 110 of the participants, going down to 137 mg/dL and 6.43%, respectively.

The ketogenic diet over three months led to a remarkable reduction in HbA1c levels and to great improvements in symptoms associated with type 2 diabetes. This is an especially important finding for diabetes patients in India, because with the Indian diet people eat carbohydrates morning, noon, and night, and we want to encourage and counsel people to change these dietary habits."

Kanchana Lakshmi Prasanna Angati, MD