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Guiding Clients Following Very Low-Carb Diets for Diabetes
By Anne Danahy, MS, RDN
If you work with patients who have diabetes, chances are they’ve asked about the ketogenic diet or very low-carbohydrate diets to improve their blood sugar levels. While this very strict way of eating isn’t right for everyone, research suggests a keto diet can provide metabolic benefits. Thus, it might be a useful tool for some people.

However, there are downsides to this way of eating besides having to say goodbye to pasta and fruit. Very low-carbohydrate diets can cause short-term side effects and potential longer-term adverse nutrition-related health implications. Educating patients about how to navigate these can help them be more successful with such an eating pattern.

Keto Diets and Glycemic Control
A ketogenic diet limits carbohydrates to 5% to 10% of calories. It provides adequate protein (1 to 1.2 g/kg) and 70% to 75% calories from fat, or enough to satisfy one’s appetite.1 This macronutrient distribution limits glucose and forces the body to use fat, in the form of ketones, as fuel.

To maintain ketone production, called nutritional ketosis, carbohydrates are limited to 20 to 50 g/day.1 That can present a challenge for many, depending on their usual carbohydrate intake and dietary preferences. However, if clients follow the diet properly, a growing body of research suggests it can help with glycemic control.

Currently, most trials have been small and short term, but they’ve been promising.2,3 In its 2019 consensus statement, the American Diabetes Association stated that “very low-carbohydrate eating patterns have been shown to reduce A1c and the need for antihyperglycemic medications.”4 

Other metabolic benefits identified in the research include reductions in blood pressure and triglycerides and an increase in HDL cholesterol. LDL cholesterol often increases, but it’s a less atherogenic LDL particle size.1-3,5   

The Adverse Effects of Nutritional Ketosis
Very low-carb diets are presumed to be safe in the short term. Unlike diabetic ketoacidosis, nutritional ketosis doesn’t alter blood pH.1 Still, dietitians should be aware of short-term side effects, as well as potential long-term adverse effects so they can advise patients.

The Keto Flu
The most commonly reported side effect from transitioning to a very low-carbohydrate diet is experiencing a cluster of flulike symptoms, often referred to as the keto flu.6 Symptoms are usually mild and resolve within days to a few weeks once nutritional ketosis is achieved. They can include nausea, vomiting, headache, fatigue, dizziness, insomnia, constipation, and halitosis.

Most of these symptoms occur because reduced insulin levels cause increased sodium, potassium, and fluid loss. Constipation is likely due to a decrease in fiber intake. Supplements such as medium-chain triglycerides and exogenous ketones may help reduce the time it takes to achieve nutritional ketosis and therefore keto flu symptoms, but they may exacerbate gastrointestinal distress.6 Patients may feel better during the transition by merely increasing water and electrolyte intake.7   

Long-Term Risks
There may be long-term nutrition implications due to the restrictive nature of the keto diet, although there are limited studies on adults. Some adverse effects that have been reported include the following1,3,7-9:

• inadequate vitamin/mineral intake, especially calcium, potassium, magnesium, B vitamins, and vitamin C;
• impaired bone health;
• kidney stones;
• high uric acid levels leading to gout when combined with a very low-calorie keto diet; and
• hepatic steatosis in studies on mice.

Another concern involves changes in the gut microbiome. Diet is a driving factor in the quality and diversity of the gut microbiota. A more diverse microbiota is associated with improved health and immunity—and a high fiber diet rich in fruits, vegetables, and other plant foods promotes diversity.10

The gut microbiota changes quickly in response to diet modifications. Some research shows there’s less diversity and a decrease in beneficial microbes with a ketogenic diet.10 A small study on patients who followed a keto diet for GLUT1 deficiency syndrome found that after three months on the diet, levels of bacteria associated with gut inflammation increased.11 However, other research on small groups of children with refractory epilepsy and adults with multiple sclerosis found improvements in quality and diversity after a keto diet.12 

Keto Isn’t Appropriate for Everyone
Very low-carb or keto diets are contraindicated in certain groups. They include the following9:

• people with lipid metabolism disorders;
• individuals who have had a heart attack or stroke within the past year;
• women who are pregnant or breast-feeding;
• people with kidney or liver disease;
• anyone with alcohol or substance abuse;
• individuals with eating disorders;
• those with type 1 diabetes or type 2 diabetes with beta-cell dysfunction/failure; and
• people with diabetes who take SGLT2 inhibitors (eg, empagliflozin and canagliflozin), because of increased risk of euglycemic diabetic ketoacidosis.

Advice for Patients
Patients who are motivated to follow a keto diet for metabolic health likely will have better adherence and results if they work with a dietitian. Nutrition therapy should address the short-term side effects of transitioning into nutritional ketosis as well as meal planning to maintain gut health, prevent gastrointestinal symptoms, and meet vitamin and mineral needs.

The following are some teaching points for dietitians:

• Increase fluid and electrolyte intake, especially in the beginning stages.
• After initial nutritional ketosis is achieved, patients should experiment with their carbohydrate intake and check ketones to determine their carbohydrate threshold.
• Although this is a high-fat diet, the quality of fat counts. Limit saturated fat and incorporate mostly unsaturated fats from plant-based sources such as olive oil, avocados, olives, nuts, and seeds.
• To prevent constipation and maintain gut health, eat high fiber vegetables with each meal. Focus on incorporating prebiotic-rich vegetables such as garlic, onions, asparagus, and jicama.
• Choose lean proteins such as chicken over meats high in saturated fat.
• Incorporate fatty fish high in omega-3s such as salmon, sardines, mackerel, or anchovies.
• Remind patients to take supplements as needed.
• If patients decide a keto diet isn’t right for them, encourage them to transition off slowly and develop a plan for how to eat afterwards.

RDs also should tell clients that there are limited long-term studies on potential adverse effects regarding very low-carbohydrate and keto diets, but there may be risks. And don’t forget that there’s no one-size-fits-all diet. Twenty to 50 g of carbs might be too restrictive for some people, but 75 to 90 g may be doable for others and still provide excellent results.

— Anne Danahy, MS, RDN, is an integrative nutritionist and freelance writer with Dietitian Pros, premier nutrition staffing. Dietitian Pros provides nationwide class-leading nutrition staffing services and recruits registered dietitians to serve in temporary, part-time or full-time positions.


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