Researchers wanted to know if a food survey could accurately measure how much fat people eat. They compared what 58 Australian adults reported eating with measurements from their red blood cells, which reflect long-term fat intake. The survey did a decent job matching up with the blood cell measurements for most types of fat, though it wasn’t perfect. This suggests the survey can be useful for tracking fat intake, but doctors and researchers should be careful when people report eating extreme amounts of fat or use supplements.

The Quick Take

  • What they studied: Whether a food survey accurately measures the amount and types of fat people eat by comparing survey answers to fat levels found in red blood cells
  • Who participated: 58 healthy Australian adults (67% women, average age 40 years) who completed a food survey and had their blood tested
  • Key finding: The survey showed moderate agreement with blood cell measurements for most types of fat (correlation scores of 0.26-0.59), meaning it’s reasonably accurate but not perfect
  • What it means for you: Food surveys can help track your fat intake fairly well, but they work best for people eating typical amounts of fat. If you take fish oil supplements or eat extreme amounts of fat, the survey may be less accurate. Talk to your doctor about which method works best for your situation.

The Research Details

Researchers recruited 58 healthy Australian adults and asked them to fill out a detailed food survey about their fat intake. At the same time, they took blood samples and measured the types and amounts of fat in the participants’ red blood cells using a lab technique called gas chromatography. Red blood cells are useful because the fat in their membranes reflects what someone has eaten over the past few months, making them a good comparison point for checking if surveys are accurate.

The researchers then compared the fat intake numbers from the surveys with the fat measurements from the blood cells. They used statistical tools to see how well the two methods matched up. They also looked at whether other factors—like how many carbohydrates people ate or whether they took supplements—affected how well the survey matched the blood results.

Food surveys are one of the most common ways doctors and researchers learn about what people eat, but people sometimes forget foods or estimate portions incorrectly. By comparing surveys to an objective biological marker (fat in red blood cells), scientists can figure out whether surveys are trustworthy. This helps researchers know whether they can rely on survey data when studying how diet affects health.

This study had a reasonable sample size of 58 people and used a well-established lab method to measure blood fat accurately. However, the study only included healthy Australian adults, so results may not apply to other groups. The moderate agreement scores suggest the survey is useful but has room for improvement. The study was published in a peer-reviewed nutrition journal, indicating it met scientific standards.

What the Results Show

The food survey showed moderate agreement with red blood cell fat measurements for most types of fat studied. Saturated fat (the kind found in butter and meat) had the strongest agreement, meaning the survey was most accurate for this type. Unsaturated fats and omega-3 fats showed weaker but still moderate agreement. When researchers adjusted their analysis for other factors like age and carbohydrate intake, the agreement generally stayed about the same or got slightly weaker, except for saturated fat which remained moderately accurate.

The study found that people taking omega-3 supplements (like fish oil pills) had weaker agreement between their survey answers and blood measurements. This makes sense because supplements add fat to the body in ways that surveys might not capture well. Interestingly, the amount of carbohydrates people ate had the least effect on how well the survey matched the blood results.

The researchers looked at specific types of omega-3 fats (EPA, DHA, and DPA) and linoleic acid separately. These showed moderate agreement with the survey, though not as strong as saturated fat. The study also revealed that the survey worked better for people eating typical amounts of fat but became less reliable for those reporting very high or very low fat intakes.

This study adds to existing research showing that food surveys can be reasonably accurate for measuring fat intake but aren’t perfect. Previous studies have used similar approaches comparing surveys to blood measurements, and this Australian study confirms those general findings while providing specific information for the Australian population.

The study only included 58 people, which is a relatively small group, so results may not apply to everyone. All participants were healthy adults, so the findings may not work for people with health conditions or different diets. The study only looked at Australian adults, so the survey may work differently in other countries. People taking supplements had less accurate survey results, which limits how useful the survey is for that group. The researchers note that the body can make some fats on its own, which the survey can’t measure, so the comparison isn’t perfect.

The Bottom Line

The Australian Eating Survey food frequency questionnaire can be used as a reasonable tool to measure fat intake in healthy Australian adults (moderate confidence). It works best for saturated fat and typical fat intakes. For people taking supplements or eating extreme amounts of fat, combine the survey with blood tests for better accuracy (moderate confidence). If you’re tracking your fat intake for health reasons, use this survey as one tool but discuss results with your doctor (moderate confidence).

This research matters for doctors and researchers studying how diet affects health in Australian populations. It’s useful for people wanting to track their fat intake accurately. People taking fish oil or other fat supplements should know the survey may be less accurate for them. This research is less relevant for people outside Australia or those with specific health conditions not studied here.

Red blood cell fat measurements reflect eating patterns over about 2-3 months, so you’d need to follow a consistent diet for that long to see accurate results. Changes in fat intake would take several weeks to show up in blood cell measurements.

Want to Apply This Research?

  • Log your daily fat intake using the app’s food diary, then compare your weekly totals to blood test results every 8-12 weeks. Track separately: saturated fats, unsaturated fats, and omega-3 fats. Note any supplements you’re taking, as they affect accuracy.
  • Use the app to set a target for saturated fat intake (since the survey is most accurate for this type), then log meals daily. The app can send reminders to log meals consistently, which improves survey accuracy. If taking supplements, log them separately so you remember to mention them to your doctor.
  • Check your logged fat intake against your blood test results every 2-3 months. If they don’t match well, review your logging accuracy with the app’s help. Track whether adding or removing supplements changes how well your survey data matches blood results. Use the app’s trend feature to see if your fat intake is consistent over time.

This study shows that food surveys can reasonably measure fat intake but aren’t perfect, especially for people taking supplements or eating extreme amounts of fat. These findings apply to healthy Australian adults and may not apply to other groups. Before making major changes to your diet based on fat intake measurements, talk to your doctor or registered dietitian. This research is for educational purposes and should not replace professional medical advice. If you have health conditions affecting fat metabolism or take medications, consult your healthcare provider before using survey-based dietary assessments.