Some healthy habits clash with your medicines, so check these goals first

Key takeaways

• In a trial of nearly 21,000 people in rural China, a potassium-based salt substitute cut strokes and deaths, but the study left out people with kidney disease and people taking potassium-sparing diuretics or potassium pills.
• In a 2018 trial, fasting two days a week about doubled the rate of low blood sugar in people taking diabetes medicines, even after their doses were lowered.
• If you take warfarin, NIH says to keep vitamin K steady; half a cup of boiled collard greens holds about 530 micrograms, several times an adult’s daily need.
• About 14% of U.S. adults have chronic kidney disease, and CDC estimates that 87% of them don’t know it, so get basic labs before a big diet change.
• The fix is usually a change in medicine or method, not giving up the goal, so bring the goal and your full medicine list to your clinician.

In rural China, researchers assigned 300 of 600 villages to swap their cooking salt for a substitute made of 75% sodium chloride and 25% potassium chloride, while the rest kept regular salt².

The nearly 21,000 people in the study, called SSaSS, were older adults with high blood pressure or a past stroke¹. Over almost five years, the salt-substitute group had fewer strokes, fewer major heart and blood vessel events, and fewer deaths¹. Strokes ran at about 29 per 1,000 people per year with the substitute, versus about 34 with regular salt¹. Serious problems from high potassium were about as common in both groups¹.

That result makes a wellness goal look simple: swap the salt. But the trial excluded people with known kidney disease and people who took potassium-sparing diuretics or potassium pills¹². It also didn’t check blood potassium along the way².

Those are the people NIH warns about. Damaged kidneys and several common blood pressure drugs hold potassium in the body, and too much potassium can affect the heart³⁴.

Same shaker, two different answers. That’s the pattern behind this guide: many popular wellness moves are healthy for most people and risky for a few. The goal usually survives, but the method may need a clinician’s input first.

“Healthy for most people” describes an average, and you may not know your fine print

Studies often leave out people whose health could make a change unsafe, as SSaSS did². That protects volunteers, but it means a headline finding may say nothing about someone like you.

The catch is that you may not know you belong to an excluded group. CDC estimates that about 14% of U.S. adults have chronic kidney disease, based on national survey data from 2021 to 2023⁵. About 87% of adults with it don’t know they have it⁵.

So get a recent checkup and basic blood work before a big change in how you eat, fast or take supplements. Our article on preventive care explains which screenings usually cost nothing.

Many natural-health traditions start from the idea that no two bodies are alike, which is why a good practitioner asks about your history before suggesting anything. Checking your medical fine print is the same idea, with lab numbers. Respecting your body includes respecting your chart.

Fasting and low-carb eating can drop blood sugar too far on some diabetes drugs

Fasting and cutting carbohydrates help some people with type 2 diabetes⁷⁸. The trouble is the medicines.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says insulin can cause low blood sugar, called hypoglycemia, and so can pills that push the pancreas to release insulin, such as sulfonylureas and meglitinides⁶. Skipping or delaying meals, eating too few carbohydrates, or fasting while still taking these medicines raises the risk⁶.

For many people with diabetes, a reading below 70 mg/dL counts as low⁶. Early signs include shakiness, hunger, dizziness, confusion, irritability, a racing heartbeat and headache⁶. Severe lows can cause fainting or seizures⁶.

A 2018 trial in the journal Diabetic Medicine shows the size of the effect. Forty-one adults with type 2 diabetes ate about 500 to 600 calories on two days a week for 12 weeks⁷. Their medicines were cut back, and they got education. Even so, fasting about doubled the rate of hypoglycemia⁷.

Weight, blood sugar and quality of life improved, and with the dose cuts and teaching, lows were fewer than the team expected⁷. That was a supervised plan, not a solo experiment.

Low-carb eating raises a second issue. A 2021 review in Frontiers in Nutrition lays out a medicine plan for it, and its source matters. The authors, from West Virginia University, Cleveland Clinic and a Vancouver nutrition institute, wrote for an international working group that promotes low-carb diets to put type 2 diabetes into remission⁸. They reported no commercial conflicts⁸.

The group advises stopping sulfonylureas at the start and, in most cases, cutting total insulin by about half (less if blood sugar is very high), then checking glucose often and adjusting⁸. The authors say the insulin figure comes from clinical experience, and they note that published guidance on scaling back diabetes drugs is thin⁸.

The same review flags SGLT2 inhibitors, a newer class of diabetes pills. These drugs can cause ketoacidosis, a dangerous buildup of acids in the blood, even when blood sugar looks normal⁸. A very low-carb diet may add to that risk, and the authors suggest stopping these drugs in many people who eat 30 to 50 grams of carbohydrate a day or less⁸.

None of this means people with diabetes can’t fast or go low-carb. It means the medicine plan has to change with the food plan, ideally before day one. Our articles on faith and fasting and on extreme fasting cover religious fasts and long water fasts.

On warfarin, the danger is a sudden change in greens, not the greens

Warfarin, sold as Coumadin, prevents clots by working against vitamin K⁹. NIH’s Office of Dietary Supplements (ODS) says people on warfarin and similar drugs should keep vitamin K intake steady, from food and supplements. Sudden changes can make the drug stronger or weaker⁹.

Some foods carry a lot. Half a cup of boiled frozen collards has about 530 micrograms, and a cup of raw spinach about 145⁹. Three ounces of natto, a fermented soybean food, has about 850⁹. Adult women need about 90 micrograms a day and men about 120⁹.

Picture a hypothetical reader who starts a daily green smoothie in January to eat cleaner. On warfarin, that’s a big jump in vitamin K, the kind of swing ODS warns about⁹.

MedlinePlus, the National Library of Medicine’s consumer site, says to limit large amounts of leafy greens and certain vegetable oils and to talk with your doctor before changing your diet¹⁰.

MedlinePlus also lists nonprescription and herbal products that may interact with warfarin. They include coenzyme Q10, echinacea, garlic, ginkgo, ginseng, goldenseal and St. John’s wort, plus pain relievers such as aspirin and ibuprofen¹⁰. Ask about alcohol and grapefruit too¹⁰.

If you want to eat more greens, tell the team that checks your clotting tests before you start, not after.

With kidney disease, more protein and potassium aren’t automatically better

High-protein shakes and bars are everywhere. For people with chronic kidney disease (CKD), NIDDK says the amount matters. Some people need a moderate amount of protein so wastes don’t build up in the blood, while too little can cause malnutrition⁴. People on dialysis may need more⁴.

Potassium is the bigger surprise. Potassium-rich foods are a standard heart-health tip. But damaged kidneys can struggle to clear potassium, and levels that run too high or too low can affect the heart and muscles⁴. NIDDK suggests seasoning with herbs and spices instead of salt substitutes, which can be high in potassium, and limiting foods that list potassium chloride⁴.

ODS adds that salt substitutes range from about 440 to 2,800 milligrams of potassium per teaspoon³. Several common drugs make the body hold on to potassium³:

• ACE inhibitors, such as benazepril
• ARBs, such as losartan
• Potassium-sparing diuretics, such as spironolactone and amiloride

ODS also names type 1 diabetes, heart failure, adrenal insufficiency and liver disease as conditions that raise the risk of high potassium³. For people with CKD, even potassium below the usual daily target can be too much³.

There’s good news inside the caution. Medicare covers medical nutrition therapy, one-on-one counseling with a registered dietitian, for people with CKD who have a doctor’s referral⁴. A kidney dietitian can help you keep the spirit of a whole-food plan while fitting your lab numbers.

Heart failure can turn “drink more water” into a problem

Hydration challenges tell you to drink more, and then more. With heart failure, the body often holds on to fluid, so the American Heart Association (AHA) says your care team might limit how much you drink¹¹. Ask for your daily number.

The early-warning system AHA recommends is a scale. Weigh in each morning on the same one, after the bathroom and before you eat¹¹. A gain of 5 pounds or more in a week, or 2 to 3 pounds a day several days in a row, is a reason to call, unless your team gave you a different number¹¹.

Exercise helps the heart, but the right dose is personal. AHA recommends regular moderate activity, suggests checking with your clinician first if you aren’t active, and points to cardiac rehab teams that can build a plan¹¹. If you drink alcohol, AHA suggests asking whether it’s safe for you at all¹¹.

Antioxidant pills during cancer treatment raised a red flag

Antioxidant pills sound protective, but during chemotherapy they may get in the way. SWOG, a cancer clinical trials network, studied 1,134 people in a breast cancer chemotherapy trial who answered questions about supplements¹². Those who took antioxidant supplements both before and during chemo were 41% more likely to see their cancer return¹². The list included vitamins A, C and E, carotenoids and coenzyme Q10¹².

Vitamin B12, iron and omega-3 supplements were also linked to more recurrence and death¹². Multivitamins were not¹².

The study was observational, meaning it found a link but can’t prove the pills caused harm¹². Lead author Christine Ambrosone of Roswell Park Comprehensive Cancer Center advised getting nutrients, antioxidants included, from food and talking with your doctor about supplements¹².

The National Cancer Institute (NCI), in a fact sheet last reviewed in 2017, says trials of antioxidant supplements during cancer treatment have had mixed results, with worse outcomes in some, especially among smokers¹³. Its advice is to use them with caution and tell your doctors about every supplement¹³. Prevention trials backfired too. In two large studies, beta-carotene pills, alone or with vitamin A, raised lung cancer rates in smokers¹³.

Pregnancy and an eating-disorder history change the plan too

Some nutrient-dense foods carry a pregnancy warning. ODS says too much preformed vitamin A, the form in animal foods and many supplements, can cause birth defects affecting the eyes, skull, lungs and heart¹⁴. Experts advise pregnant women not to take high-dose vitamin A supplements above 3,000 micrograms a day¹⁴.

Three ounces of pan-fried beef liver holds about 6,582 micrograms, more than twice that amount¹⁴. Beta-carotene, the plant form, isn’t known to cause birth defects¹⁴. If you’re pregnant or trying to be, run any new fast, diet or supplement stack past your prenatal provider.

An eating-disorder history calls for the same care. Goals built on restriction, fasting windows, calorie counting or strict “clean” rules can look like ordinary health goals. Talk them over with your treatment team before you start.

The National Alliance for Eating Disorders runs a free helpline staffed by licensed therapists who specialize in eating disorders, at 1-866-662-1235, on weekdays from 9 a.m. to 7 p.m. Eastern¹⁵. It offers support and referrals, not emergency help¹⁵. If you’re in crisis or thinking of harming yourself, call or text the 988 Suicide and Crisis Lifeline, or call 911.

The check-first table

If a row fits you, talk with your clinician or pharmacist before you start, and bring the question in the last column.

If your goal is…	Check first if you…	Why it matters	Ask this
Fasting or skipping meals	Take insulin, a sulfonylurea or a meglitinide	Lows are more likely without food67	“How should my doses change on fasting days?”
Very low-carb or keto eating	Take insulin, a sulfonylurea or an SGLT2 inhibitor	Lows, and ketoacidosis with normal-looking sugar8	“Which medicine changes before I start?”
Switching to a potassium salt substitute	Have kidney disease, heart failure or type 1 diabetes, or take an ACE inhibitor, ARB, spironolactone or amiloride	Potassium can build up34	“Are my potassium and kidney numbers safe for this?”
Eating far more leafy greens	Take warfarin	Vitamin K swings change clotting910	“How do we keep my clotting tests steady?”
High-protein eating or shakes	Have kidney disease	Some need moderate protein; dialysis changes needs4	“What amount of protein fits my kidneys?”
Drinking much more water	Have heart failure	Fluids may need a limit11	“What is my daily fluid limit?”
Starting harder exercise	Have heart failure and aren’t active	The right dose is personal11	“Would cardiac rehab fit me?”
Adding antioxidants or other supplements	Are in chemotherapy or radiation	Possible interference with treatment1213	“Which supplements should I pause?”
Liver, or high-dose vitamin A	Are pregnant or could be	Birth defect risk14	“How much vitamin A is right for me?”
Fasting, tracking or strict food rules	Have an eating-disorder history	Restriction can blur into symptoms	“Does this fit my recovery plan?”

What the evidence shows

Claim	Evidence rating	What it rests on
A potassium-based salt substitute lowers stroke and death in older adults with high blood pressure or a past stroke, without kidney disease	Strong evidence	Large randomized trial of nearly 21,000 people in rural China12
Potassium salt substitutes are safe for people with kidney disease or on potassium-holding drugs	Not enough evidence	These groups were excluded from SSaSS; NIH advises caution or avoidance234
Fasting raises the risk of low blood sugar for people on glucose-lowering drugs	Strong evidence	NIH guidance; rate about doubled in a 2018 randomized trial despite dose cuts67
One fixed rule, such as halving insulin, is the right low-carb start for everyone	Not enough evidence	Clinical experience, not trials; the review itself suggests cuts of about 30% to 50%, then adjusting by glucose readings8
Sudden changes in vitamin K change how warfarin works	Strong evidence	Well-established interaction described by NIH910
Antioxidant supplements during chemotherapy may raise the chance of recurrence	Promising but early	One large observational study and mixed trials1213
Beta-carotene pills prevent lung cancer in smokers	Evidence says no, or unsafe	Two large trials found higher lung cancer rates13
High-dose preformed vitamin A is safe in pregnancy	Evidence says no, or unsafe	Linked to birth defects; experts cited by NIH advise against supplements above 3,000 micrograms a day14

Questions readers ask

The bottom line

Most wellness goals don’t need permission. A few need a plan. If you take insulin or certain diabetes pills, warfarin, potassium-holding blood pressure drugs, or cancer treatment, or if you have kidney disease, heart failure, a pregnancy or an eating-disorder history, check before you change how you eat, fast, drink or supplement.

The check is rarely a “no.” More often it’s a dose change, a lab test, a target number or a safer version of the same idea. The healthiest habit is the one that fits your body, including the parts written in your chart.

Related reading

• What happens when you don’t tell your doctor about supplements
• What to bring, write down and ask before a doctor visit
• Fasting windows help some people eat less, while long fasts add real risks
• Faith shapes how people eat, fast and decide, and your clinician should know
• A stack of safe supplements can add up to an unsafe dose

Sources

1. American College of Cardiology. “Salt Substitute and Stroke Study – SSaSS” (trial summary of Neal B, Wu Y, Feng X, et al., New England Journal of Medicine, 2021). ACC, 2021. acc.org
2. Lamberg M, Cohoon KP. “Salt Less, Live Longer: Results of the Salt Substitute and Stroke Study.” American College of Cardiology, October 2021. acc.org
3. NIH Office of Dietary Supplements. “Potassium: Fact Sheet for Health Professionals.” ODS, updated June 2, 2022. ods.od.nih.gov
4. National Institute of Diabetes and Digestive and Kidney Diseases. “Eating Right for Chronic Kidney Disease.” NIDDK, reviewed January 2025. niddk.nih.gov
5. Centers for Disease Control and Prevention. “Chronic Kidney Disease in the United States” (data and research). CDC, March 2026. cdc.gov
6. National Institute of Diabetes and Digestive and Kidney Diseases. “Low Blood Glucose (Hypoglycemia).” NIDDK, reviewed July 2021. niddk.nih.gov
7. Corley BT, Carroll RW, Hall RM, Weatherall M, Parry-Strong A, Krebs JD. “Intermittent Fasting in Type 2 Diabetes Mellitus and the Risk of Hypoglycaemia: A Randomized Controlled Trial.” Diabetic Medicine, 2018;35(5):588-594. ourarchive.otago.ac.nz
8. Cucuzzella M, Riley K, Isaacs D, on behalf of the International Working Group on Remission of Type 2 Diabetes. “Adapting Medication for Type 2 Diabetes to a Low Carbohydrate Diet.” Frontiers in Nutrition, 2021;8:688540. frontiersin.org
9. NIH Office of Dietary Supplements. “Vitamin K: Fact Sheet for Health Professionals.” ODS, updated March 29, 2021. ods.od.nih.gov
10. MedlinePlus, National Library of Medicine. “Warfarin.” MedlinePlus, revised March 15, 2026. medlineplus.gov
11. American Heart Association. “Lifestyle Changes for Heart Failure.” AHA, reviewed June 16, 2025. heart.org
12. SWOG Cancer Research Network. “Antioxidant Use During Chemo Risky” (news release on Ambrosone CB, et al., Journal of Clinical Oncology). SWOG, December 19, 2019. swog.org
13. National Cancer Institute. “Antioxidants and Cancer Prevention.” NCI, reviewed February 6, 2017. cancer.gov
14. NIH Office of Dietary Supplements. “Vitamin A and Carotenoids: Fact Sheet for Health Professionals.” ODS, updated March 10, 2025. ods.od.nih.gov
15. National Alliance for Eating Disorders. “What Is an Eating Disorder Helpline?” The Alliance, updated July 30, 2024. allianceforeatingdisorders.com