Researchers studied 69 African American women with obesity to understand how their bodies burn calories differently on low-carb versus low-fat diets. After 10 weeks, both diets led to similar weight loss of about 6 pounds. However, the study found something interesting: women with lower insulin sensitivity (a measure of how well their body handles blood sugar) lost more weight on low-carb diets because their bodies didn’t slow down their metabolism as much. This suggests that the type of diet that works best might depend on individual body chemistry, not just calories alone.

The Quick Take

  • What they studied: Whether low-carb and low-fat diets affect how many calories your body burns differently, especially in African American women
  • Who participated: 69 African American women with obesity who were randomly assigned to eat either a low-carb or low-fat diet for 10 weeks, with 40 completing the full study
  • Key finding: Women with lower insulin sensitivity (difficulty managing blood sugar) burned more calories and lost more fat on low-carb diets because their metabolism didn’t slow down as much compared to low-fat diets
  • What it means for you: If you have difficulty managing blood sugar, a low-carb diet might help you lose weight more effectively than a low-fat diet. However, this finding is specific to African American women and may not apply to everyone. Talk to your doctor about which diet approach is best for your individual health situation.

The Research Details

This was a carefully controlled research study where 69 African American women with obesity were randomly assigned to follow either a low-carb or low-fat diet for 10 weeks. All food was provided to the participants to ensure they followed the diet correctly. After the diet ended, there was a 4-week period where participants ate enough food to maintain their new weight. At the beginning and end of the study, researchers measured several things: how well their bodies handled blood sugar (insulin sensitivity), their body composition (muscle versus fat), and how many calories they burned at rest and during daily activities.

Understanding how different diets affect your metabolism is important because it helps explain why the same diet doesn’t work equally well for everyone. By measuring actual calorie burn rather than just assuming everyone’s metabolism works the same way, researchers can give better personalized advice. This study focused specifically on African American women because previous research suggests their bodies may respond differently to diets than other groups.

This study was a randomized controlled trial, which is considered a strong research design. The researchers provided all food to participants, which means they could be sure people were actually following the diet. They used precise scientific methods to measure calorie burn and body composition rather than relying on estimates. However, only 40 of the 69 women completed the study, which is a limitation. The study was relatively short (10 weeks), so we don’t know if these results would hold up over months or years.

What the Results Show

Both the low-carb and low-fat diets resulted in similar weight loss, with participants losing an average of 6.3 pounds. This shows that both diets can work for weight loss when calories are controlled. However, the study found an important difference in how the body responded: women with lower insulin sensitivity (meaning their bodies struggle more with blood sugar control) experienced better results on the low-carb diet. Specifically, these women’s metabolisms didn’t slow down as much on low-carb diets compared to low-fat diets. On low-fat diets, women with lower insulin sensitivity showed their bodies burned about 202 fewer calories per day than expected (adaptive thermogenesis), but on low-carb diets, this slowdown didn’t happen. This difference is significant because when your metabolism slows down, it becomes harder to lose weight and keep it off.

Women with better insulin sensitivity (meaning their bodies handle blood sugar well) showed the opposite pattern—their metabolism slowed down more on low-carb diets than low-fat diets. This suggests that the best diet choice really depends on your individual body chemistry. The study also measured changes in body composition and found that the diets affected fat loss differently depending on insulin sensitivity, though both groups lost weight overall.

Previous research has suggested that low-carb diets might work better for weight loss, but this study helps explain why: for people with insulin sensitivity issues, low-carb diets don’t trigger the metabolic slowdown that often happens with calorie restriction. This finding adds nuance to the debate about which diet is ‘best’—it appears the answer depends on your individual metabolism. The focus on African American women is important because most diet research has been done on white populations, and this study shows that results may differ across racial groups.

The study only lasted 10 weeks plus 4 weeks of weight maintenance, so we don’t know if these results continue over longer periods. Only 40 of 69 women completed the study, which could affect the results. The study was relatively small, so findings may not apply to all African American women. The research was conducted in a controlled setting where all food was provided, which is different from real life where people choose their own foods. Finally, the study measured insulin sensitivity in a specific way (intravenous glucose tolerance test) that may not reflect everyday blood sugar control.

The Bottom Line

If you are an African American woman with obesity and have lower insulin sensitivity (difficulty managing blood sugar), a low-carb diet may be worth trying as it appears to support better weight loss without your metabolism slowing down as much. However, this recommendation is based on one study and should be discussed with your doctor or registered dietitian. If you have better insulin sensitivity, the choice between low-carb and low-fat may matter less. Both diets can work for weight loss when calories are controlled.

This research is most relevant to African American women with obesity who are trying to lose weight, especially those who know they have insulin sensitivity issues or prediabetes. The findings may also be interesting to healthcare providers working with this population. People of other racial backgrounds should be cautious about assuming these results apply to them, as the study was specific to African American women. Anyone considering a major diet change should consult with their healthcare provider first.

In this study, participants lost weight over 10 weeks on both diets. However, real-world weight loss timelines vary greatly depending on starting weight, how strictly you follow the diet, and other lifestyle factors. Most people can expect to see initial changes within 2-4 weeks, but significant weight loss typically takes several months. The metabolic benefits described in this study (not having your metabolism slow down as much) would theoretically help with long-term weight management, but this study didn’t measure results beyond 13 weeks.

Want to Apply This Research?

  • Track daily carbohydrate intake (grams per day) and weight weekly. For users with lower insulin sensitivity, monitor how energy levels and hunger change when carbs are reduced. Note any changes in cravings or blood sugar symptoms if applicable.
  • If you have lower insulin sensitivity, consider gradually reducing refined carbohydrates (bread, pasta, sugary foods) and replacing them with protein and healthy fats. Start by identifying your highest-carb meals and making one substitution per week rather than overhauling your entire diet at once.
  • Measure weight weekly (same day, same time), track carb intake daily, and rate energy levels and hunger on a 1-10 scale. After 4-6 weeks, review whether you’re seeing consistent weight loss and improved energy. If not seeing results, consider consulting a dietitian to ensure the diet is appropriate for your individual needs.

This research is informational only and should not replace professional medical advice. The findings apply specifically to African American women and may not apply to other populations. Before starting any new diet, especially if you have diabetes, prediabetes, or other health conditions, consult with your doctor or registered dietitian. This study was relatively short-term, so long-term effects are unknown. Individual results vary greatly based on genetics, lifestyle, and other factors. If you experience any concerning symptoms while changing your diet, stop and contact your healthcare provider immediately.