Ketogenic and Low-Carbohydrate Diets: What the Latest Evidence Really Shows

A balanced, evidence-based look at ketogenic and low-carbohydrate eating—showing the types of nutrient-dense, low-carb foods commonly used in these diets.

Patients regularly ask whether ketogenic or low-carbohydrate diets are worth trying—for weight loss, diabetes control, inflammation, or overall metabolic health. These diets remain incredibly popular, but like most nutrition approaches, the truth is more nuanced than the hype. Some people benefit greatly; others develop risks that shouldn’t be ignored.

Below is a clear, evidence-informed overview of what these diets are, how they work, where they help, where they can cause problems, and what we still don’t know.

What Ketosis Actually Is — and Why It Matters

A ketogenic diet is built around creating ketosis, a normal metabolic state your body enters when carbohydrate intake becomes very low—typically ≤50 grams per day. When glucose availability drops, insulin levels fall, and the liver begins breaking down fat into ketones, including beta-hydroxybutyrate, acetoacetate, and acetone. These ketones become an alternative fuel for the brain, heart, kidneys, and skeletal muscle.

This shift from carbohydrate-burning to fat-burning can reduce appetite, improve insulin sensitivity, stabilize blood sugar, and accelerate initial weight loss. Most people enter ketosis within 24–72 hours of limiting carbohydrates, although hydration and individual metabolism affect the transition.

It’s important to distinguish nutritional ketosis, which produces safe, mild ketone elevations (0.5–3.0 mmol/L), from diabetic ketoacidosis, a medical emergency seen mainly in people with type 1 diabetes when ketones and blood acidity rise dangerously. Ketogenic diets do not cause ketoacidosis in individuals with normal insulin function.

What These Diets Actually Are

A ketogenic diet is a very low-carbohydrate, high-fat diet—usually <10% of calories from carbohydrates or ≤50 grams per day. The classic clinical version uses a 4:1 ratio of fats to the combined amount of protein and carbohydrates. Modified versions, including the popular Atkins-style plan, allow closer to 10% of calories from carbohydrates.

A low-carbohydrate diet is less restrictive—typically 50–150 grams of carbs per day or <45% of total energy. These diets may not produce ketosis but still significantly lower carbohydrate intake.

Where These Diets Have Strongest Evidence

1. Short-Term Weight Loss

Ketogenic and low-carbohydrate diets often outperform balanced diets in the first 3–6 months. Adults with overweight or obesity tend to lose the most weight when carbohydrates are kept ≤50 grams/day.

2. Improved Blood Sugar and Insulin

These diets consistently reduce:

• fasting glucose

• insulin levels

• HbA1c

• triglycerides

• and increase HDL cholesterol

For patients with type 2 diabetes or metabolic syndrome, the improvements can be significant.

3. Neurologic Benefits

The ketogenic diet remains a proven therapy for drug-resistant epilepsy. Emerging evidence suggests potential improvements in:

• cognitive symptoms in Alzheimer’s

• motor symptoms in Parkinson’s

• migraine frequency and severity

These findings are promising but still early.

Who Benefits the Most

Research shows the strongest benefits in:

• adults with overweight or obesity

• patients with type 2 diabetes or prediabetes

• individuals with metabolic syndrome

• patients with drug-resistant epilepsy

For these groups, metabolic improvements often outweigh the risks—especially short-term.

Risks and Adverse Effects

1. LDL Cholesterol Increases

One of the most consistent findings is that ketogenic diets raise LDL cholesterol—on average by 8–9 mg/dL.In some individuals, especially lean adults, the increase may be far more dramatic.

2. “Keto Flu”

Common early symptoms include headache, fatigue, nausea, constipation, diarrhea, and lightheadedness.

3. Nutrient Gaps

Because these diets limit many plant foods, people may develop low:

• potassium

• magnesium

• calcium

• vitamin D

• fiber

4. Kidney and Liver Concerns

Individuals with underlying kidney or liver disease should avoid strict carbohydrate restriction unless medically supervised.

5. Reduced Exercise Capacity

Some people feel reduced stamina during ketosis—especially for high-intensity exercise.

6. Mortality Curves

Observational studies show a U-shaped mortality curve: both very low and very high carbohydrate intakes are associated with increased mortality.

Long-Term Results: Benefits Fade Over Time

The early advantages largely diminish by 6–12 months. At 12–24 months, ketogenic and balanced diets produce similar:

• weight loss

• blood pressure changes

• LDL cholesterol

• HbA1c

• metabolic improvements

Long-term adherence is a major limitation. Many people stop due to food monotony, GI symptoms, or difficulty maintaining the required restriction.

The LDL Cholesterol Puzzle: Why Baseline Weight Matters

A major recent discovery is that LDL response depends heavily on baseline BMI.

A 2024 analysis found:

• Normal-weight adults (BMI <25): LDL ↑ ~41 mg/dL

• Adults with BMI ≥35: LDL ↓ slightly

Normal-weight adults also experience consistent increases in:

• total cholesterol

• apolipoprotein B

• atherogenic LDL particles

These findings raise important questions about long-term cardiovascular risk for lean adults on ketogenic diets.

The Ketogenic Diet Trial: The Most Important Study Underway

With so many unanswered questions, one ongoing study is particularly significant.

What This Trial Is

The Ketogenic Diet Trial is a prospective observational study following 100 relatively lean individuals who developed LDL-C >190 mg/dL after starting a ketogenic diet but otherwise maintain excellent metabolic health.

This is the first study to directly examine whether diet-induced LDL increases translate into coronary atherosclerosis progression.

Study Design

Participants undergo serial coronary CT angiography (CCTA) over 12 months to assess:

• calcified plaque

• non-calcified plaque

• total plaque burden

Participants must:

• be relatively lean

• continue their ketogenic diet

• have LDL-C >190 mg/dL

• maintain otherwise favorable metabolic markers

This population is distinct from traditional hypercholesterolemia patients, who usually have multiple risk factors.

Why the Study Matters

Ketogenic diets often improve:

• triglycerides

• HDL cholesterol

• glucose

• insulin sensitivity

• inflammation

• blood pressure

—but can dramatically raise LDL cholesterol.

This creates a unique clinical dilemma: Does LDL behave the same way in someone whose other metabolic risk factors improve?

Status

No results are yet available. Data analysis will begin after the trial concludes.

Why Clinicians Are Watching Closely

The trial aims to answer whether LDL increases seen in lean ketogenic-diet adopters—sometimes 40+ mg/dL or even 100 mg/dL—lead to measurable progression of coronary plaque.

This will help determine:

• whether diet-induced LDL elevation is truly atherogenic

• whether guidelines should be modified for this population

• whether lipid-lowering therapy is warranted

Until results are available, counseling these patients remains challenging.

Bottom Line

Ketogenic and low-carbohydrate diets can be powerful short-term metabolic tools, especially for patients with type 2 diabetes, metabolic syndrome, or obesity. But they are not universal solutions, and they come with real cautions—particularly regarding LDL cholesterol and long-term sustainability.

Until more long-term cardiovascular and imaging data are available:

• personalize the dietary approach

• monitor lipids carefully

• do not assume that “good metabolic markers” eliminate LDL risk

• avoid extreme carbohydrate restriction in lean individuals without close supervision

Used thoughtfully, ketogenic and low-carbohydrate diets can be effective—but they should be tailored to the individual, not prescribed by default.