- A two-day oatmeal-only diet resulted in lower cholesterol levels that persisted for six weeks in a new study.
- In the study, the sudden influx of oats led to beneficial gut microbiome activity that may disrupt cholesterol handling at the cellular level.
- A parallel six-week study by the same researchers, which replaced one meal a day with oats, did not observe similar cholesterol reductions.
People who followed a low-calorie diet consisting primarily of oatmeal for two days experienced a long-lasting reduction in LDL (“bad”) and total cholesterol levels in a clinical trial.
The reduced levels of cholesterol remained in effect for six weeks after the two-day diet.
LDL levels were reduced by 10%, less than the amount achievable with medication, but nonetheless significant.
The first trial investigated the effect of the two-day oatmeal diet, and involved 32 women and men who either followed the oatmeal diet or served as controls following a standard calorie-reduction diet of the same duration.
The 17 people on the oatmeal diet ate 300 grams of oatmeal per day. They were allowed to supplement the cereal with vegetables or fruit. Altogether, they consumed half their normal number of calories. After the two-day oatmeal regimen, dieters returned to their habitual diet without oats.
Oatmeal dieters lost two kilograms of weight and saw a slight reduction in blood pressure immediately after the two-day period.
The second trial explored the effect of integrating oats on a regular basis into one’s diet. Seventeen people replaced one daily meal with oats — in their choice of porridge, oatmeal, smoothies, or baked goods — for six weeks while maintaining their overall typical daily caloric intake. The 17 members of the control group in this trial did not change their typical diet, except that they made sure not to consume oats.
The researchers found that simply including oats into a daily meal plan did not produce measurable changes in LDL or overall cholesterol levels after six weeks.
The implication of the study is that a short, intensive consumption of oats may be more effective at reducing cholesterol than incorporating oats into your diet on a regular basis.
Junior Professor Marie-Christine Simon, of Universität, Bonn in Germany, is the study’s senior investigator. She said the intense exposure to oats delivered by the two-day diet resulted in a strong response by the gut microbiome.
Simon explained the “dose and rapid exposure to oat components — especially phenolic compounds that are metabolized by the gut microbiota — can trigger stronger biochemical responses than a modest daily intake.”
Specifically, she proposed, “The high-dose diet delivers a much larger quantity of oat phenolics and fiber than a single regular meal. This generates higher levels of substrates (like ferulic acid) for microbial metabolism.”
This was borne out in fecal samples collected for the study, Simon reported. “This large oat load significantly increased microbially produced phenolic metabolites, especially dihydroferulic acid, which were associated with the cholesterol reduction.”
In addition, the suddenness of the influx of oats, Simon proposed, “likely induced quick shifts in gut microbial metabolic activity, producing more bioactive compounds that can enter circulation and influence host lipid metabolism.”
Overall, this suggests that the phenolics can disrupt cholesterol handling at the cellular level.
As to whether repeating a brief oatmeal diet periodically would help a person control their cholesterol, Simon was optimistic but cautious:
“It would be scientifically reasonable to hypothesize that repeated short-term high-dose oat interventions might yield recurring or sustained LDL reduction and possibly influence weight and blood pressure, especially if gut metabolic pathways are consistently engaged — but this remains to be tested in future RCTs (“randomized, controlled trials”).
The study’s findings do not mean that consuming oats on a daily basis has no role to play in helping a person control cholesterol levels alongside appropriate medications prescribed by one’s doctor.
Michelle Routhenstein, MS, RD, CDCES, CDN, is a registered dietitian who specializes in heart disease. She noted, “In small, tightly managed settings, it is easier to observe pronounced short-term changes than the more gradual LDL improvements typically seen when oats are incorporated into everyday, free-living diets, where many other factors are also at play.”
Routhenstein also cautioned in the study, “the follow-up period based on self-reported habitual intake cannot fully disentangle the effects of oats from subtle improvements in overall diet quality or changes in weight that may also contribute to lower LDL levels.”
“From a real-world perspective, the takeaway remains reassuring,” she said.
“Regularly including moderate amounts of oats within a heart-healthy eating pattern, alongside other sources of soluble fiber, plant protein, and overall nutrient adequacy, continues to be a practical and evidence-based way to support LDL lowering and cardiometabolic health, without the need for extreme or short-term dietary approaches.”
— Michelle Routhenstein, MS, RD, CDCES, CDN
Routhenstein already recommends oats for her clients seeking to control cholesterol, “but as one component of a broader, plant-forward, high–viscous-fiber eating pattern, rather than as a magic bullet.”
She explained that oats also support the gut microbiome by providing beta-glucan. “Meta-analyses show that about 3 grams per day of oat beta-glucan, usually from two to three servings of oats or oat bran, can lower LDL by roughly 5–10%,” Routhenstein pointed out.
“Oats are not unique,” she added. “Barley has comparable beta-glucan and similar LDL-lowering effects, and whole-grain rye and other viscous-fiber-rich grains can also provide modest cholesterol benefits.” These grains provide other healthy nutrients as well.