Question: How consistently do low-carbohydrate diets lead to significant metabolic improvements in a real-world setting?
Takeaway: This 2019 study, drawn from an internet survey of self-reported low-carb diet adherents, found more than half the subjects lost at least 20 pounds, and the share of subjects with a healthy HbA1c increased from 12% to 68%. These changes occurred alongside additional improvements in multiple self-reported measures related to mobility and quality of life. The results rely on self-reported data from a self-selected sample of low-carb dieters and thus likely represent a “best-case” estimate of the impact of low-carbohydrate diets in a free-living population. Despite this and other significant caveats related to self-reported data, the fact that these patients regularly achieved outcomes rarely met through pharmacotherapy — including sustainable reversal of metabolic and mental disease — indicates the low-carbohydrate diet has meaningful clinical utility.
Currently, more than two-thirds of Americans are overweight, and one-third are obese (1). More than 30 million Americans are diabetic and 100 million are prediabetic (2). Treatment of diabetes and its related comorbidities accounts for one in every three Medicare dollars and one in every five health-care dollars spent (3). The metabolic syndrome, or “carbohydrate intolerance” as some have called it (4), is associated with a variety of specific maladies, including inflammation, vascular dysfunction, NAFLD, POCS, sleep apnea, and a general decline in health (5). Most mainstream diabetes organizations frame diabetes as a purely progressive condition that inevitably leads to a decline in health and organ failure (6). This is, in fact, consistent with the effectiveness of diabetes treatment using traditional approaches; a Kaiser Permanente study found only 0.007% of subjects reversed their diabetes without bariatric surgery over seven years (7).
Low-carbohydrate diets are increasingly well established as a tool to reverse metabolic disease, including diabetes (8). For example, one recent trial found more than half of diabetic patients who adhered to a ketogenic diet reduced their HbA1c to nondiabetic levels and were able to stop taking glucose-lowering medication and/or insulin (9). Low-carbohydrate diets have been discouraged by some of the same diabetes organizations noted above, often due to the fact that they increase total and LDL cholesterol and are thereby thought to increase heart disease risk. These same diets also, however, generally increase HDL, reduce triglycerides, and so reduce the HDL:TG ratio. This ratio has been found to be more predictive of heart disease risk than either LDL or total cholesterol, both of which have received only weak and inconsistent support as markers for heart disease risk or risk modification targets in more recent studies (10).
In light of this evidence, this 2019 survey assessed the impact of a low-carbohydrate diet on weight, health, and quality of life.
Researchers surveyed 1,580 subjects who were sourced through social media and word of mouth, primarily through the networks of clinicians who prescribed low-carbohydrate diets for weight loss and health improvement. Subjects were surveyed to assess the amount of carbohydrate they consumed each day; the impact of a low-carbohydrate diet on their body weight and a variety of biomarkers; and the impact of a low-carbohydrate diet on subjective measures of well-being, independence, and quality of life.
Approximately 80% of those surveyed reported following a diet that would be expected to induce ketosis, consuming fewer than 50 grams of carbohydrate per day. Three out of four subjects initiated the diet primarily to lose weight, and a smaller percentage sought improvements to chronic disease symptoms and energy levels.
More than one-third of subjects lost at least 30 pounds following a low-carb diet, and nearly three-quarters lost at least 10 pounds. As shown in the figure below, weight loss was greater among subjects who restricted carbohydrate intake to a greater extent, with more than half of all subjects who ate fewer than 50 grams of carbohydrate per day losing at least 20 pounds.
Weight loss was well maintained among the subjects surveyed, with more than half of those who remained on the diet for at least two years reporting a loss of 20 pounds or more.
Glycemic control improved substantially as well. Prior to initiating the diet, 48.5% of subjects had a diabetic HbA1c (> 6.5%), and only 16.6% had normal HbA1c (< 5.5%). The low-carb diet reversed these proportions, with 65.3% of subjects reporting a normal HbA1c after following the low-carb diet and only 7.1% remaining diabetic. As was true of weight loss on the diet, greater carbohydrate restriction led to greater glycemic improvements, with the rate of HbA1c normalization greatest among those consuming fewer than 30 grams of carbohydrate per day.
Subjects reported significant reductions in medication use. The share of subjects using antidepressants (12.5% to 5.8%), anti-anxiety medication (7.3% to 3.4%), sleep aids (11.4% to 4.8%), painkillers (22.1% to 5.0%), or anti-inflammatory medication (27.1% to 6.8%) all decreased significantly.
Subjects also reported significant improvement across a variety of measures of quality of life. Energy levels improved in many subjects, with the majority of subjects reporting low energy levels prior to initiating a low-carb diet and high energy levels after following the diet for at least one year (See Table 4 and Figure 5 below). There were significant reductions in the share of subjects who reported problems completing daily activities (22.0% to 2.7%); moderate or severe mobility problems (17.2% to 3.0%); moderate, severe, or extreme pain or discomfort (42.6% to 4.9%); and moderate, severe, or extreme anxiety or depression (33.4% to 3.9%). In addition to improving quality of life, these changes have been associated with improved longevity (11) and are consistent with previous evidence indicating low-carbohydrate diets may be a promising treatment option to improve mental health without pharmacotherapy (12).
Subjects also reported they experienced less hunger, tiredness, difficulty concentrating, or irritability between meals on a low-carb diet than they had on their previous diet.
While subjects’ total cholesterol and LDL cholesterol increased, HDL cholesterol increased from 57 to 71 mg/dL while triglyceride levels dropped from 149 to 82 mg/dL. As noted above, these changes — in particular, the reduction in the TG:HDL ratio from 3.49 to 1.37 — reflect a reduction in overall cardiovascular risk.
Subjects also reported anecdotal improvements across a variety of other conditions for which low-carb diets have provided benefits, including migraines (13), IBS (14), heartburn (15), POCS (16), NAFLD (17), and chronic pain (18).
This study is confounded by major potential biases. As the study drew data from self-selected subjects sourced through channels favorable to low-carb diets (i.e., the networks of clinicians known to prescribe low-carb diets), these subjects were almost certainly more compliant and received more positive results than a representative selection of low-carb dieters. Much of the data was derived from self-reporting, which may introduce additional deviation from actual clinical changes.
With these caveats in mind, however, it remains clear that low-carb diets can, in at least some subjects, generate greater improvements in metabolic health, mental health, functionality, and quality of life than generally can be achieved by traditional therapies. The survey indicates the core premises associated with some of these conditions — such as the belief that diabetes is irreversible — are unfounded. It also indicates low-carb diets have the potential for substantial clinical benefit and are worth consideration by patients or clinicians looking to improve metabolic, mental, or overall health.
- National diabetes statistics report, 2017; Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 mo.; Prevalence of obesity among adults and youth: United States, 2011–2014; Trends in obesity among adults in the United States, 2005 to 2014
- Metabolic effects of the very-low-carbohydrate diets: Misunderstood ‘villains’ of human metabolism
- The economic burden of elevated blood glucose levels in 2012: Diagnosed and undiagnosed diabetes, gestational diabetes mellitus, and prediabetes; Economic costs of diabetes in the U.S. in 2012
- Relationship between fasting plasma insulin level and resistance to insulin-mediated glucose uptake in normal and diabetic subjects; Relationship between fasting plasma insulin level and resistance to insulin-mediated glucose uptake in normal and diabetic subjects
- Metabolic syndrome and risk of incident cardiovascular events and death; Insulin resistance and coronary heart disease in nondiabetic individuals; Inflammation as a link between obesity, metabolic syndrome and type 2 diabetes; Endothelial dysfunction in metabolic syndrome: Prevalence, pathogenesis and management; Metabolic syndrome: Nonalcoholic fatty liver disease; The metabolic syndrome in polycystic ovary syndrome; Obstructive sleep apnea, inflammation, and the metabolic syndrome; Metabolic syndrome and risk of cancer: A systematic review and meta-analysis; Metabolic syndrome and the risk of mild cognitive impairment and progression to dementia: Follow-up of the Singapore longitudinal ageing study cohort; Metabolic syndrome, mild cognitive impairment, and progression to dementia. The Italian Longitudinal Study on Aging
- U.K. Prospective Diabetes Study 16: Overview of 6 years’ therapy of type II diabetes: A progressive disease; Classification and diagnosis of diabetes; Late stage complications of diabetes and insulin resistance
- Incidence of remission in adults with type 2 diabetes: The diabetes & aging study
- Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: A systematic review and meta-analysis; Dietary carbohydrate restriction as the first approach in diabetes management: Critical review and evidence base; Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet; Pretreatment fasting plasma glucose and insulin modify dietary weight loss success: Results from 3 randomized clinical trials; An online intervention comparing a very low-carbohydrate ketogenic diet and lifestyle recommendations versus a plate method diet in overweight individuals with type 2 diabetes: A randomized controlled trial; The effects of a low-carbohydrate diet vs. a low-fat diet on novel cardiovascular risk factors: A randomized controlled trial; Spanish ketogenic Mediterranean diet: A healthy cardiovascular diet for weight loss; Dietary intervention for overweight and obese adults: Comparison of low-carbohydrate and low-fat diets. A meta-analysis; Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: The A to Z weight loss study: A randomized trial; Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet; In type 2 diabetes, randomisation to advice to follow a low-carbohydrate diet transiently improves glycaemic control compared with advice to follow a low-fat diet producing a similar weight loss; Effects of low-carbohydrate and low-fat diets: A randomized trial; The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: One-year follow-up of a randomized trial; Comparison of low- and high-carbohydrate diets for type 2 diabetes management: A randomized trial; Effects of a low-carbohydrate diet on weight loss and cardiovascular risk factor in overweight adolescents
- A novel intervention including individualized nutritional recommendations reduces hemoglobin A1c level, medication use, and weight in type 2 diabetes
- Fasting triglycerides, high-density lipoprotein, and risk of myocardial infarction; Use of metabolic markers to identify overweight individuals who are insulin resistant; High ratio of triglycerides to HDL-cholesterol predicts extensive coronary disease; Metabolic abnormalities: Triglyceride and low-density lipoprotein; Saturated fats versus polyunsaturated fats versus carbohydrates for cardiovascular disease prevention and treatment; Ratio of triglycerides to HDL cholesterol is an indicator of LDL particle size in patients with type 2 diabetes and normal HDL cholesterol levels; Does the association of the triglyceride to high-density lipoprotein cholesterol ratio with fasting serum insulin differ by race/ethnicity; Hyperinsulinemia as an independent risk factor for ischemic heart disease; Low-fat dietary pattern and risk of cardiovascular disease: The women’s health initiative randomized controlled dietary modification trial; Multiple Risk Factor Intervention Trial. Risk factor changes and mortality results. Multiple Risk Factor Intervention Trial Research Group; Dietary carbohydrate restriction induces a unique metabolic state positively affecting atherogenic dyslipidemia, fatty acid partitioning, and metabolic syndrome; Lack of an association or an inverse association between low-density-lipoprotein cholesterol and mortality in the elderly: A systematic review
- Muscular strength as a strong predictor of mortality: A narrative review; How fast does the grim reaper walk? Receiver operating characteristics curve analysis in healthy men aged 70 and over; Association between muscular strength and mortality in men: Prospective cohort study; Ability to sit and rise from the floor as a predictor of all-cause mortality; Primary care of patients with chronic pain; Treating depression and anxiety in primary care
- Management of depression in older adults: A review; The current status of the ketogenic diet in psychiatry
- Migraine improvement during short lasting ketogenesis: A proof-of-concept study
- A very low-carbohydrate diet improves symptoms and quality of life in diarrhea-predominant irritable bowel syndrome
- A very low-carbohydrate diet improves gastroesophageal reflux and its symptoms
- The effects of a low-carbohydrate, ketogenic diet on the polycystic ovary syndrome: A pilot study
- The effect of a low-carbohydrate, ketogenic diet on nonalcoholic fatty liver disease: A pilot study
- Ketogenic diets and pain