Both Low-Fat and Low-Carb Diets Tied to Less Heart Disease
•February 11, 2026
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Why It Matters
The findings shift the focus from low‑carb versus low‑fat debates to overall food quality, guiding clinicians, policymakers, and the food industry toward healthier product formulations and recommendations.
Key Takeaways
- •High-quality low-carb diets lower heart disease risk
- •Unhealthy low-fat diets increase coronary risk
- •Plant-based, whole foods drive cardioprotective effects
- •Study emphasizes diet quality over macronutrient composition
- •Findings question guidelines promoting full-fat dairy, animal protein
Pulse Analysis
The long‑standing controversy over whether low‑carbohydrate or low‑fat diets are better for heart health has finally found common ground in a new study published in JACC. Researchers tracked over 200,000 participants from the Health Professionals Follow‑Up Study and two Nurses’ Health Studies for three decades, creating detailed low‑carb and low‑fat indices that distinguished healthy from unhealthy food choices. Their analysis revealed that when these diets are built around whole grains, legumes, fruits, vegetables, and unsaturated fats, they cut coronary heart disease risk by up to 15 percent, regardless of whether carbs or fats are restricted.
Beyond the headline numbers, the study’s metabolomic sub‑analysis showed that high‑quality low‑carb and low‑fat diets improve triglyceride levels, lower C‑reactive protein, and produce a favorable plasma metabolite profile. These shared biological pathways suggest that the protective effect stems from nutrient density rather than macronutrient balance. The results echo recent shifts in dietary guidance that prioritize whole, minimally processed foods and align with AHA recommendations emphasizing plant‑based proteins and healthy fats, while casting doubt on newer USDA guidelines that endorse full‑fat dairy and higher animal protein intake.
For the food industry and health‑policy makers, the implications are clear: product reformulation should focus on reducing added sugars, refined grains, and saturated fats while boosting fiber‑rich, plant‑forward ingredients. Consumers seeking heart‑healthy options can prioritize diet quality over strict macro counts, easing adherence and expanding market demand for clean‑label, nutrient‑dense foods. As insurers and employers increasingly tie wellness incentives to evidence‑based nutrition, the study provides a data‑driven roadmap for aligning commercial offerings with cardiovascular risk reduction.
Both Low-fat and Low-carb Diets Tied to Less Heart Disease
There’s a lot of nuance in the numbers, though—only diets with a lot of healthy, nutrient-dense foods came out as winners.
Eating either a low‑carbohydrate or low‑fat diet is associated with a lower risk of coronary heart disease (CHD) over roughly 30 years of follow‑up, but the devil really is in the details of these popular dietary patterns, according to results from a study published today in JACC.
Low‑carb and low‑fat diets that included unhealthy foods—those with a greater emphasis on animal protein, animal fat, and low‑quality carbohydrates, such as highly processed foods with added sugars and refined grains—were associated with an increased risk of CHD. High‑quality versions of those diets emphasizing plant‑based foods, whole grains, and unsaturated fats were cardioprotective.
“These two diets are widely practiced in the US as well as many other countries for things like glucose control and overall metabolic health, but the effects of these two diets on reducing heart disease has been a topic of ongoing debate,” lead investigator Zhiyuan Wu, PhD (Harvard T.H. Chan School of Public Health, Boston, MA), told TCTMD. “One potential reason is that people can follow the same type of low‑carb or low‑fat diets using either healthy or unhealthy foods.”
In the US, there is a lot of interest in the relative benefits of both low‑carb and low‑fat diets, with no shortage of opinion on which is best. This new study suggests that as long as the quality of the macronutrients is equivalent, the composition doesn’t matter as much.
“Focusing on the overall diet quality may offer flexibility for people to choose what aligns with their own preferences while still supporting heart health,” said Wu.
Earlier this year, the US government released new Dietary Guidelines for Americans. The message in the pared‑down document was to eat real food. While the premise of selecting whole, nutrient‑dense foods over highly processed items was applauded, the guidelines broke with previous recommendations that focused on protein from plant sources. Unlike in the past, the dietary guidelines now advise Americans to also eat protein from animal sources and to consume full‑fat dairy, something that nutrition experts have criticized.
“I think our conclusions largely align with the evolving emphasis on diet quality in the new dietary guidelines,” said Wu. Like prior versions, the US guidelines “encourage whole, nutrient‑dense food and limiting ultraprocessed food, especially refined carbohydrates and sugar. This is what our findings largely support.”
With respect to animal protein and full‑fat dairy, though, the results don’t line up with the new recommendations.
“Our findings, together with a substantial body of existing evidence, do suggest that higher intake of saturated fat and animal protein, largely from red meat and full‑fat dairy, are associated with a higher risk of disease,” said Wu. “Our results reinforce the health benefits of plant‑based proteins and fat, which is consistent with several other popular dietary patterns like DASH and the AHA recommendations.”
Nutrition expert Alice Lichtenstein, DSc (Tufts University, Boston), who wasn’t involved in the research, noted that diets with a greater emphasis on animal protein and animal fat were associated with a higher risk of CHD in the study.
“I think if you look at the data where there’s the predominantly animal‑based diet versus a vegetable‑based diet, the vegetable‑based diet does better,” she said, pointing out that there’s a large steak with fat featured prominently in the new visual schematic that’s part of US dietary guidelines.
Still, Lichtenstein is hopeful the new study will put the focus on healthy foods, which is also the goal of the current dietary guidelines.
“At least the dietary guidelines prior to this, and some of the positive aspects of what the US government released, is that you really need to think about the individual foods,” she said. “If you eat carbohydrates, it’s best to choose whole grain. If you’re going to consume fruits and vegetables, and hopefully people do that, then it should be in the least processed form.”
Risks of Unhealthy Diets
For the study, the researchers assessed the incidence of CHD associated with different dietary patterns in three large‑scale cohort studies: 42,720 men in the Health Professionals Follow‑Up Study (HPFS), 64,164 women in the Nurses’ Health Study (NHS), and 91,589 women in Nurses’ Health Study II (NHSII). Since enrollment, participants have completed detailed food‑frequency questionnaires (FFQs) every couple of years, with five low‑carb and five low‑fat indices derived from the FFQ assessments.
These indices, based on dietary composition and macronutrient quality, included: total low‑carb diet (LCD), animal‑based LCD, vegetable‑based LCD, healthy LCD, and unhealthy LCD; as well as total low‑fat diet (LFD), animal‑based LFD, vegetable‑based LFD, healthy LFD, and unhealthy LFD. Scores were developed based on macronutrient intake, such that those with a high LCD and high LFD scores consumed lower carbohydrate and fat content, respectively. The unhealthy LCD was based on the amount of animal fat and protein in the diet, whereas the unhealthy LFD included more simple sugars and processed grains and less fruit, legumes, and whole grains.
The researchers also performed a lifestyle validation substudy in men and women to examine the relationship between these dietary indices and a plasma metabolome of more than 300 metabolites.
When comparing participants with the highest LCD score (reflective of the lowest carbohydrate consumption) against those with the lowest LCD score, the pooled multivariable‑adjusted hazard ratios for CHD were:
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Total LCD: 1.05 (95 % CI 1.01‑1.10)
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Animal LCD: 1.07 (95 % CI 1.02‑1.12)
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Vegetable LCD: 0.94 (95 % CI 0.90‑0.99)
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Unhealthy LCD: 1.14 (95 % CI 1.09‑1.20)
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Healthy LCD: 0.85 (95 % CI 0.82‑0.89)
For those with the highest LFD score (reflective of the lowest fat intake) compared with those with the lowest LFD score, the adjusted hazard ratios for CHD were:
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Total LFD: 0.93 (95 % CI 0.89‑0.98)
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Animal LFD: 0.94 (95 % CI 0.90‑0.98)
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Vegetable LFD: 0.87 (95 % CI 0.83‑0.91)
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Unhealthy LFD: 1.12 (95 % CI 1.07‑1.17)
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Healthy LFD: 0.87 (95 % CI 0.83‑0.91)
Overall, the LCD was linked to a slightly higher risk of CHD, but there was a reduction in risk for those who consumed a vegetable‑based LCD and those who consumed a healthy version of the diet. The animal‑based LCD was associated with increased CHD risk.
With respect to LFD, there was an overall reduction in CHD risk, with benefit seen among those who consumed animal‑ and vegetable‑based versions, as well as those who consumed a healthy LFD. An unhealthy low‑fat diet was associated with a significantly increased CHD risk.
To TCTMD, Wu noted that the reduction in CHD risk was comparable with the high‑quality, nutrient‑dense versions of the LCD and LFD, “even though these two diets emphasized totally different macronutrients.”
Both healthy versions of the diets were associated with lower triglyceride and high‑sensitivity C‑reactive protein levels and an improved metabolomic profile. This improved metabolomic profile with both LCD and LFD suggests shared biological mechanisms in which macronutrient quality affects health risk.
Do Results Support New Dietary Guidelines?
On the whole, Lichtenstein was impressed by the study’s methodology and findings. “It reinforced something that I’ve been saying for a long time, which is the quality of the food, not whether it’s high or low in this or that macronutrient, is important,” she commented.
The nutrition field, she said, is increasingly moving past the debate between LCD versus LFD to emphasize dietary quality, just as was recommended in the 2021 dietary guidance from the AHA. In that AHA statement, which Lichtenstein chaired, dietary quality was stressed over individual foods or nutrients.
“I don’t think the major recommendation of anyone is to go to extreme on either end. Whether it’s low‑fat, high‑fat, or whether it’s a vegan diet versus a Mediterranean diet versus the DASH diet versus the US Department of Agriculture diet, there’s a tremendous amount of overlap. Sometimes these different diets are presented as unique, but when you really drill down, there’s an immense amount of commonality.”
Both Wu and Lichtenstein stressed that these diets do not reflect extreme versions of the low‑carb or low‑fat craze, such as the keto diet, but rather reflect more moderate eating patterns of people enrolled in the three cohort studies.
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