According to Gram Research analysis of 47 randomized trials involving 3,450 adults, low-carb, high-fat diets produce modest weight loss and improve triglycerides and HDL cholesterol, but ketogenic diets raise LDL cholesterol by 0.43 mmol/L. High-carb diets increase triglycerides by 0.24 mmol/L. Research shows no single macronutrient distribution works best for everyone—the optimal diet depends on your individual cholesterol, blood sugar, and weight profile.
A major analysis of 47 studies involving 3,450 people compared how different diets affect heart health. Researchers found that low-carb, high-fat diets help people lose weight and improve certain cholesterol levels, but they also raise LDL (bad) cholesterol in some cases. Meanwhile, high-carb diets can increase triglycerides, another type of blood fat. The key finding: there’s no single “best” diet for everyone. What works depends on your individual health profile and the quality of foods you choose, not just whether you eat more carbs or fat.
Key Statistics
A 2026 network meta-analysis of 47 randomized trials involving 3,450 adults found that low-carb, high-fat diets reduced body mass index by 0.48 kg/m² compared to low-fat diets, though effects on blood pressure and blood sugar were minimal.
According to research reviewed by Gram, ketogenic diets increased LDL cholesterol by 0.43 mmol/L and total cholesterol by 0.55 mmol/L compared to moderate-carbohydrate diets, while also raising HDL cholesterol by 0.12 mmol/L.
A 2026 analysis of 47 clinical trials found that high-carbohydrate diets increased triglycerides by 0.24 mmol/L compared to moderate-carbohydrate diets in adults with cardiovascular disease risk factors.
Research shows that carbohydrate restriction improves triglycerides and HDL cholesterol but is not consistently favorable for LDL cholesterol, demonstrating distinct trade-offs between different macronutrient-focused dietary patterns.
The Quick Take
- What they studied: How different combinations of carbohydrates and fats affect heart disease risk factors like cholesterol, blood pressure, weight, and blood sugar in adults over 35.
- Who participated: 3,450 adults aged 35-75 years old who had at least one risk factor for heart disease, from 47 different research studies conducted between 2013 and 2025.
- Key finding: Low-carb, high-fat diets reduced body weight slightly (about half a kilogram per square meter of body surface) and improved some cholesterol markers, but increased LDL cholesterol in ketogenic diets. High-carb diets increased triglycerides (blood fats) by 0.24 mmol/L.
- What it means for you: If you’re considering a diet change for heart health, focus on the quality of foods rather than just cutting carbs or fat. Work with your doctor to choose a diet that matches your specific health numbers and goals, since no single approach works best for everyone.
The Research Details
Researchers conducted a network meta-analysis, which is a sophisticated way of combining results from many different studies to find patterns. They searched scientific databases for all randomized controlled trials (the gold standard of research) published between January 2013 and October 2025 that tested specific diets with clear carbohydrate and fat targets in adults at risk for heart disease.
They organized 47 studies into groups based on how much carbohydrate and fat each diet contained. They used a low-fat, moderate-carbohydrate diet as their reference point—the baseline they compared everything else against. Then they used statistical methods to estimate how each diet type affected various heart health markers like cholesterol levels, body weight, waist size, blood pressure, and blood sugar control.
The analysis was careful to account for differences between studies and to measure the certainty of their findings using confidence intervals, which show the range where the true effect likely falls.
This approach is important because individual studies can sometimes give conflicting results, and people often wonder which diet is truly best. By combining 47 studies with thousands of participants, researchers can see the bigger picture and identify consistent patterns. This method also reveals trade-offs—where one diet might help one health marker but hurt another—which is crucial for real-world decision-making.
This is a high-quality analysis because it included only randomized controlled trials (the most reliable study type), had a large combined sample size of 3,450 people, and covered a recent 12-year period of research. The researchers were transparent about their methods and clearly defined their dietary categories. However, the quality depends on the individual studies included, and results may not apply equally to all populations or age groups.
What the Results Show
Low-carb, high-fat diets produced modest weight loss compared to low-fat diets, reducing body mass index by about 0.48 kg/m². This is a small but measurable effect. These diets also improved HDL cholesterol (the “good” kind) and reduced triglycerides, which are important for heart health.
However, ketogenic diets (the strictest low-carb approach) raised LDL cholesterol (the “bad” kind) by 0.43 mmol/L and total cholesterol by 0.55 mmol/L. This is concerning because high LDL cholesterol increases heart disease risk. The good news is that ketogenic diets also raised HDL cholesterol by 0.12 mmol/L, which partially offsets the LDL increase.
High-carbohydrate diets increased triglycerides by 0.24 mmol/L compared to moderate-carb diets. Elevated triglycerides are another risk factor for heart disease. Interestingly, different diet types had minimal effects on waist circumference, blood pressure, and blood sugar control—areas where people often expect to see bigger changes.
The analysis revealed important trade-offs: you can’t optimize all heart health markers simultaneously with diet alone. Carbohydrate restriction improved some markers (weight, triglycerides, HDL) but worsened others (LDL cholesterol in ketogenic approaches). The quality of fats consumed (monounsaturated fats were considered a marker of better diet quality) appeared important, suggesting that not all high-fat diets are created equal. The research also showed that macronutrient distribution alone—simply changing carb-to-fat ratios—had limited impact on blood pressure and blood sugar, indicating that food choices and overall diet quality matter more than macro percentages.
This research confirms what many previous studies have suggested: there’s no universally superior diet for heart health. It builds on earlier work by systematically comparing multiple diet types simultaneously rather than just pitting low-carb against low-fat. The finding that ketogenic diets raise LDL cholesterol aligns with some previous concerns, while the modest weight loss benefits of low-carb diets are consistent with earlier research. This analysis adds nuance by emphasizing that diet quality and individual metabolic profiles matter more than macronutrient ratios alone.
The studies included were mostly conducted in developed countries, so results may not apply equally to other populations. Most participants were middle-aged or older adults with existing heart disease risk factors, so findings may differ for younger, healthier people. The analysis couldn’t account for how well people actually stuck to diets in real life—people often don’t follow diets perfectly. Additionally, studies varied in length, quality, and how they measured outcomes, which can affect overall conclusions. The research also couldn’t determine which diet is best for specific individuals without knowing their complete health picture.
The Bottom Line
For adults with heart disease risk factors: Consider a diet emphasizing whole foods and healthy fats (olive oil, nuts, fish) rather than focusing solely on carb or fat percentages. If you’re overweight, a moderate low-carb approach may help with weight loss. If you have high triglycerides, reducing refined carbohydrates may help. If you have high LDL cholesterol, be cautious with very-low-carb ketogenic diets and prioritize unsaturated fats. Work with your doctor or dietitian to choose an approach matching your specific cholesterol, blood pressure, and blood sugar numbers. These recommendations have moderate-to-strong evidence support.
Adults aged 35-75 with at least one heart disease risk factor (high cholesterol, high blood pressure, overweight, or prediabetes) should pay attention to these findings. People considering ketogenic diets should be especially aware of potential LDL cholesterol increases. Those with high triglycerides may benefit from carbohydrate reduction. However, these findings are less directly applicable to young, healthy adults without risk factors, or to people with certain medical conditions requiring specific dietary approaches.
Weight loss effects from low-carb diets typically appear within 2-4 weeks but continue gradually over 3-6 months. Cholesterol and triglyceride changes usually take 4-8 weeks to become apparent. Blood pressure improvements, if they occur, typically develop over 4-12 weeks. Most studies reviewed lasted 12 weeks to 2 years, so expect gradual changes rather than dramatic overnight results. Individual responses vary significantly based on genetics, starting health status, and diet adherence.
Frequently Asked Questions
Is a low-carb diet better for heart health than a low-fat diet?
Neither is universally better. Low-carb diets improve weight, triglycerides, and HDL cholesterol but may raise LDL cholesterol. Low-fat diets have different trade-offs. The best choice depends on your specific cholesterol, triglyceride, and blood sugar levels. Work with your doctor to choose based on your individual health profile.
Will a ketogenic diet raise my cholesterol?
Ketogenic diets typically raise both LDL (bad) and HDL (good) cholesterol. Research shows LDL increases by 0.43 mmol/L on average. The net effect on heart health depends on your baseline cholesterol levels and genetic factors. Discuss ketogenic diets with your doctor before starting, especially if you have high cholesterol.
How quickly will I see results from changing my diet?
Weight loss typically appears within 2-4 weeks, while cholesterol and triglyceride changes take 4-8 weeks. Blood pressure improvements develop over 4-12 weeks. Most benefits continue gradually over 3-6 months. Individual responses vary significantly based on genetics and diet adherence.
Does it matter what foods I eat, or just carbs versus fat?
Food quality matters significantly. The research shows that monounsaturated fats (from olive oil, nuts, fish) are better than saturated fats, and whole grains are better than refined carbs. Simply adjusting carb-to-fat ratios without improving food quality has limited effects on blood pressure and blood sugar.
Can diet alone fix my cholesterol and triglyceride problems?
Diet helps but isn’t always enough alone. The research shows modest effects on these markers from macronutrient changes. Genetics play a major role. Some people need medication alongside diet changes. Work with your doctor to develop a complete plan combining diet, exercise, and potentially medication.
Want to Apply This Research?
- Log your daily macronutrient intake (carbs, fats, protein percentages) alongside weekly measurements of weight, waist circumference, and energy levels. Track specific foods rather than just macro percentages to monitor diet quality. If possible, record lab results (cholesterol, triglycerides, blood sugar) every 3 months to see how your chosen diet affects your actual heart health markers.
- Start by identifying your primary health goal (weight loss, triglyceride reduction, or LDL cholesterol management) and choose a macronutrient balance targeting that goal. Focus on food quality first: swap refined carbs for whole grains, choose unsaturated fats over saturated fats, and increase vegetables. Use the app to experiment with different carb-to-fat ratios for 4-6 weeks, then check how you feel and review any available lab results to see what works best for your body.
- Establish a baseline of your current diet composition and health markers. Every 2 weeks, review your macro balance and how consistently you’re following your chosen approach. Monthly, assess changes in weight, energy, and how your clothes fit. Every 3 months, if possible, get lab work done to measure cholesterol, triglycerides, and blood sugar. Use the app to identify patterns—which foods and macro ratios make you feel best and produce the health improvements you’re seeking.
This research summary is for educational purposes and should not replace professional medical advice. The findings apply specifically to adults aged 35-75 with existing cardiovascular disease risk factors. Individual responses to dietary changes vary significantly based on genetics, medications, and overall health status. Before making major dietary changes, especially if you have high cholesterol, diabetes, high blood pressure, or take medications affecting cholesterol or blood sugar, consult with your doctor or registered dietitian. This analysis cannot determine the best diet for your specific situation without knowing your complete health profile and lab results.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.