Researchers studied how different foods affect special types of cholesterol in your blood that protect your heart. In a carefully controlled study of 141 people, they found that replacing carbohydrates with unsaturated fats (like olive oil) or protein changed the makeup of HDL cholesterol in ways that appear to lower heart disease risk. These changes happened within just 4 weeks. The study suggests that the type of food you eat doesn’t just affect how much cholesterol you have—it also changes what kind of cholesterol it is, and some types are much better for your heart than others.

The Quick Take

  • What they studied: Whether replacing carbohydrates with unsaturated fats or protein changes the types of good cholesterol in your blood in ways that might protect your heart
  • Who participated: 141 adults who participated in a controlled feeding study where researchers provided all their meals for 4 weeks at a time
  • Key finding: When people replaced 10% of their carbohydrate calories with unsaturated fat or protein, their blood showed increases in protective types of HDL cholesterol and decreases in less protective types—changes that suggest lower heart disease risk
  • What it means for you: Eating more unsaturated fats (like olive oil, nuts, and fish) and protein instead of refined carbohydrates may help your body create better types of cholesterol that protect your heart. However, this is one study, and you should talk to your doctor before making major diet changes

The Research Details

This was a randomized controlled trial called the OmniHeart study, which is considered one of the strongest types of nutrition research. Researchers gave 141 participants three different diets, one at a time, for 4 weeks each. The first diet was high in carbohydrates (58%), the second replaced some carbs with unsaturated fats, and the third replaced carbs with protein. The researchers controlled everything the participants ate, so they could be sure about what caused the changes in their blood. After each 4-week period, they measured 15 different types of HDL cholesterol to see how each diet affected them.

This approach is powerful because it eliminates many confusing factors—the researchers knew exactly what people were eating and could measure precise changes in their blood. The crossover design (where each person tried all three diets) is especially strong because it lets researchers compare how the same person responds to different diets.

The study focused on minor HDL subspecies, which are small variations of good cholesterol that have different jobs in your body. Some help remove bad cholesterol, some fight inflammation, and some help with blood clotting. This detailed approach goes beyond just measuring total cholesterol levels.

Most nutrition studies just measure total cholesterol, but this research looks at the specific types of cholesterol and what they actually do in your body. This matters because two people could have the same total cholesterol level but very different heart disease risk depending on which types of cholesterol they have. By understanding how different foods change these specific types, researchers can better explain why some diets protect hearts better than others.

This study has several strengths: it’s a randomized controlled trial (the gold standard for nutrition research), it controlled what people ate completely, it measured very specific types of cholesterol, and it was published in a respected journal. The main limitation is that it only lasted 4 weeks per diet, so we don’t know if these changes continue long-term. Also, 141 people is a moderate sample size—larger studies might show different patterns. The study was also done in a research setting with provided meals, which is different from how people normally eat at home.

What the Results Show

When people replaced carbohydrates with unsaturated fat, their blood showed increases in several protective types of HDL cholesterol, particularly those containing apoA2, apoE, or apoC1. These types of cholesterol are associated with lower heart disease risk based on previous research. The changes were measurable and consistent across the group.

When people replaced carbohydrates with protein, they had increases in apoE-containing HDL (another protective type) and decreases in several less protective types. Specifically, protein reduced HDL containing plasminogen, alpha-2-macroglobulin, and apoL1—types that previous studies have linked to higher heart disease risk.

The researchers also created a network map showing how these 15 different types of cholesterol are connected and how they work together. This revealed that dietary changes don’t just affect one type of cholesterol in isolation—they create coordinated changes across multiple types that work together to either increase or decrease heart disease risk.

Importantly, these changes happened within just 4 weeks, suggesting that diet can relatively quickly shift your cholesterol profile toward a more protective pattern.

The study found that unsaturated fat and protein had somewhat different effects on the cholesterol profile, even though both improved it compared to carbohydrates. Unsaturated fat seemed particularly good at increasing lipid-metabolism-related HDL types, while protein was especially effective at reducing the less protective types. This suggests that the best approach might be to include both unsaturated fats and protein in your diet, rather than choosing one or the other.

Previous research has shown that unsaturated fats and protein are better for heart health than refined carbohydrates, but scientists weren’t completely sure why. This study provides a more detailed explanation: these foods work by changing the specific types of cholesterol your body makes. The findings support the idea that the relationship between diet and heart disease is mediated through these specific cholesterol types, not just through total cholesterol levels. This aligns with recent research suggesting that minor HDL subspecies are important markers of heart disease risk.

The study only lasted 4 weeks per diet, so we don’t know if these beneficial changes continue if you eat this way for months or years. The participants were in a research setting eating provided meals, which is very different from real life where people make their own food choices and face many distractions. The study included 141 people, which is moderate-sized—larger studies might reveal different patterns or show which groups benefit most. The study measured cholesterol types but didn’t follow people to see if those with better cholesterol profiles actually had fewer heart attacks or strokes. Finally, the study replaced exactly 10% of carbohydrate calories; different amounts might produce different results.

The Bottom Line

Based on this research, consider replacing some refined carbohydrates with unsaturated fats (olive oil, avocados, nuts, fatty fish) and protein sources (chicken, fish, beans, eggs). This appears to shift your cholesterol profile in a heart-protective direction. However, this is one study showing short-term changes, so confidence is moderate. The recommendation aligns with existing heart-healthy diet guidelines, so it’s a safe change to discuss with your doctor. Don’t make drastic changes overnight—gradual shifts in eating patterns are more sustainable.

This research is most relevant for people concerned about heart disease risk, those with high cholesterol, and anyone trying to improve their diet for heart health. It’s particularly useful for people who’ve been told to eat a low-fat diet and want to understand why unsaturated fats might actually be beneficial. People with certain medical conditions (like kidney disease requiring protein restriction) should discuss dietary changes with their doctor. The findings apply to adults; we don’t know if they apply the same way to children.

The study showed changes in cholesterol types within 4 weeks, which is relatively quick. However, it typically takes 3-6 months of consistent dietary changes to see meaningful improvements in heart disease risk factors. You might not feel any different during this time—these are changes happening at the cellular level in your blood. Real benefits in terms of reduced heart disease risk would likely take years to become apparent.

Want to Apply This Research?

  • Track your daily intake of unsaturated fats (grams of olive oil, nuts, avocado, fatty fish) and protein (grams from all sources) versus refined carbohydrates. Set a goal to replace 10% of your carbohydrate calories with these foods and monitor weekly totals.
  • Use the app to log meals and identify one meal per day where you can swap a refined carbohydrate for either a healthy fat or protein source. For example: replace white bread with nuts, or swap sugary snacks for cheese and fruit.
  • Track this dietary pattern for 8-12 weeks, then get blood work done to see if your cholesterol profile has improved. Use the app to maintain consistency and identify which swaps are easiest for you to sustain long-term. Monitor energy levels and hunger to ensure the changes feel sustainable.

This research suggests potential benefits of dietary changes but does not constitute medical advice. The study measured changes in cholesterol types over 4 weeks in a controlled setting, which may not reflect real-world results. Before making significant dietary changes, especially if you have heart disease, high cholesterol, diabetes, or take medications, consult with your healthcare provider or registered dietitian. This single study should not be the only basis for dietary decisions. Individual responses to dietary changes vary, and what works for the study population may not work the same way for everyone.