Dr. Thomas Dwan - Is It Bad For You? Approved by Dr. Thomas Dwan

Are Overnight Oats Bad For You?

Also Known As: Soaked oats, Cold oatmeal



Short answer

Overnight oats are a nutritious breakfast choice rich in fiber, protein, and essential micronutrients. The base ingredients offer valuable health benefits; however, additional toppings and mix-ins can impact the nutritional profile, either enhancing or detracting from their value. When these are selected mindfully, with attention to natural sugars and overall calorie count, overnight oats can be a healthy part of a balanced diet. Personal tolerance to oats should be considered, especially for those with food sensitivities or allergies.



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Long answer

Nutrient Profile of Overnight Oats

Overnight oats are a popular breakfast choice, known for their convenience and versatility. Understanding the nutrient profile of overnight oats requires examining both the base ingredients and the potential variations in toppings and mix-ins.

At its most basic, overnight oats consist of raw oats soaked in a liquid, often milk or a milk alternative, and left to soften overnight. The primary ingredient in overnight oats are the oats themselves, which are a whole grain and provide a range of essential nutrients:

  • Dietary Fiber: Oats are particularly high in soluble fiber called beta-glucan, which has been linked to lowering cholesterol and stabilizing blood glucose levels.
  • Proteins: Oats contain a higher protein content than many other grains, which can support muscle repair and growth.
  • Fats: While oats do contain some fats, they are largely unsaturated and can contribute to heart health.
  • Vitamins and Minerals: Oats are a good source of several vitamins and minerals like manganese, phosphorus, magnesium, iron, zinc, folate, and B-vitamins.

The liquid used can also influence the nutrient profile. Dairy milk will add calcium and additional protein, while plant-based milks may provide other benefits like lower calories or enriched vitamins and minerals, depending on the type.

Add-ins and toppings can drastically alter the nutritional content of overnight oats. Ingredients like nuts and seeds add healthy fats, protein, and various micronutrients. Sweeteners (such as honey, maple syrup, or sugar), fruits (like berries or banana), and flavorings (like cocoa powder or vanilla extract) can contribute both beneficial nutrients and additional sugars. It's important to be mindful of these additions to maintain a balanced nutrient profile.

A study on the impact of processed versus whole grains highlighted the importance of consuming grains in their least processed form, which preserves their nutrient content (Reynolds et al., 2019, The Lancet). Overnight oats, made with minimally processed oats, align well with this recommendation.

Here is a basic nutrient breakdown for one serving of plain overnight oats (made with half a cup of oats and one cup of skim milk, without toppings):

Nutrient Amount
Calories ~155
Protein ~6 grams
Fat ~3 grams
Carbohydrates ~26 grams
Dietary Fiber ~4 grams
Sugars ~12 grams (from milk)
Calcium ~150-300 mg (varying by choice of milk)

It should be noted that these values can vary widely depending on the specific type of oats used (e.g., rolled, quick, steel-cut), the choice of liquid, and additional ingredients. Overall, overnight oats offer a nutritious start to the day, with a balance of macronutrients and essential micronutrients that can be tailored to individual dietary needs and preferences.

Glycemic Index and Blood Sugar Impact

The glycemic index (GI) is a valuable measure for understanding how quickly a food item can raise blood glucose levels. Foods with a high GI score may spike blood sugar rapidly, which can be detrimental over time and particularly concerning for individuals with diabetes or insulin resistance. Overnight oats, typically made with rolled or steel-cut oats, have a lower GI compared to many other breakfast choices, especially those containing refined carbohydrates. This lower GI can be attributed to the presence of complex carbohydrates and fiber in oats which slow down the absorption of sugar into the bloodstream.

When evaluating the blood sugar impact of overnight oats, it's imperative to consider the entirety of the meal's composition. The traditional base of the dish itself – raw oats soaked in water or milk – is quite stable in terms of its blood sugar impact. However, common toppings and mix-ins such as fruits, sweeteners, and additional flavor enhancers can significantly alter the final glycemic load of the meal. For instance:

  • Fruits: Adding high-fiber fruits like berries or apples can moderately increase the GI while still providing beneficial nutrients and antioxidants.
  • Sweeteners: Honey, maple syrup, or sugar can raise the GI, though alternatives like stevia or erythritol can minimize this effect.
  • Nuts and Seeds: Including nuts and seeds can help to lower the GI due to their fat and protein content, which aids in slowing down glucose absorption.

Studies such as those published in the American Journal of Clinical Nutrition suggest that the consumption of low-GI foods like oats is associated with a lower risk of developing type 2 diabetes. This is likely due in part to the beta-glucan fiber found in oats, which has been shown to improve insulin response and reduce glucose levels after meals (Hou et al., 2019).

It's also important to note that individual responses to carbohydrates can vary. What might cause a spike in blood sugar for one person can have a minimal effect on another. Thus, monitoring personal blood sugar responses to overnight oats is recommended, especially for those managing blood sugar conditions.

Including overnight oats as part of a balanced diet seems to be beneficial for most people when it comes to blood sugar management. However, it's crucial for the consumer to be mindful of the type and quantity of additional ingredients mixed into their oats to avoid any unintended increase in the GI value of their meal.

Pros and Cons of Common Toppings and Mix-ins

When it comes to enhancing the flavor and nutritional value of overnight oats, the toppings and mix-ins you choose play a vital role. Let's explore some popular choices and their potential benefits and drawbacks:

Fresh Fruit:

  • Pros: Fruits like berries, bananas, and apples are packed with vitamins, fiber, and antioxidants. They can add natural sweetness and variety to your overnight oats without the need for added sugars.
  • Cons: Some fruits are high in sugar and can contribute to a higher calorie count. Portion control is key to maintaining a balanced diet.

Nuts and Seeds:

  • Pros: Almonds, chia seeds, and flaxseeds offer a great source of healthy fats, protein, and fiber. They also provide texture and help keep you satiated for longer.
  • Cons: Nuts and seeds are dense in calories and fat, which, while healthy, can become a concern if consumed in large quantities. Measure portions to avoid excessive calorie intake.

Dried Fruit:

  • Pros: Dried fruits can be a concentrated source of nutrients and fiber. They're a convenient and shelf-stable way to sweeten your oats.
  • Cons: Many dried fruits contain added sugars and preservatives. The dehydration process also concentrates their natural sugars, potentially increasing the glycemic load.


  • Pros: Adding sweeteners like honey, maple syrup, or agave can enhance the taste of your oats and provide quick energy.
  • Cons: These sweeteners are high in sugars and calories. Overuse can lead to a sugar spike and crash, and potentially contribute to weight gain if used in excess.

Dairy and Non-Dairy Milk:

  • Pros: The liquid component of overnight oats, milk—whether dairy or plant-based—adds creaminess and provides calcium and other nutrients. Soy and almond milk can offer lower calorie alternatives with added vitamins and minerals.
  • Cons: Some non-dairy milk alternatives contain added sugars and preservatives. Dairy milk, while nutritious, may not be suitable for those with lactose intolerance or with a vegan dietary preference.


  • Pros: Yogurt is a great source of probiotics, protein, and calcium. It can make your overnight oats creamier and add a tangy flavor.
  • Cons: Flavored yogurts often contain added sugars. Full-fat versions can be high in saturated fats, which should be consumed in moderation.

Protein Powders:

  • Pros: Incorporating protein powders can boost the protein content of your meal, aiding in muscle repair and growth, and can be particularly beneficial for athletes and those looking to increase their protein intake.
  • Cons: Some protein powders may contain added sugars, artificial sweeteners, or other additives. It's important to choose a powder with minimal ingredients and to consider any dietary restrictions or allergies.

In summary, while toppings and mix-ins can elevate the taste and nutritional profile of your overnight oats, they can also introduce unwanted sugars, calories, and fats. It's essential to strike a balance and consider the overall nutritional impact these additions have on your meal. Always aim to read labels carefully and opt for the most natural, whole-food options available.

Overnight Oats and Weight Management

When it comes to weight loss or maintenance, the dietary choices we make are paramount. Overnight oats have gained popularity as a convenient and healthy breakfast option, but how do they fare in terms of weight management? Let’s break down the factors that can influence your waistline.

Caloric Content: Oats are a whole grain and considered a low-calorie food that can be beneficial for weight control. A half-cup of rolled oats, which is a common serving size for overnight oats, contains approximately 150 calories before adding any toppings or additional ingredients.

Fiber Richness: Oats are rich in a type of soluble fiber called beta-glucan. This form of fiber is noteworthy because it can help you feel full longer. Studies have shown that beta-glucan can enhance the feeling of fullness, which may help reduce overall calorie intake throughout the day. A 2016 study in the journal Nutrition Reviews highlighted the potential satiety benefits of beta-glucan in oat consumption.

Protein Content: Protein is another macronutrient known to contribute to satiety. Overnight oats can be a decent source of protein, especially when combined with milk, yogurt, or nuts. Adding these protein-rich foods can keep hunger at bay and help prevent overeating.

Glycemic Index: The glycemic index (GI) of a food indicates how quickly it raises blood sugar levels. Foods with a lower GI are preferred for weight management as they cause a slower, more controlled rise in blood sugar and insulin levels. Raw oats have a low GI, which can help manage appetite and body weight. When soaked overnight, the starches in the oats break down slightly, which may raise the GI, but they are still considered low to medium on the GI scale.

Add-Ons and Toppings: The healthfulness of overnight oats can quickly decline depending on what you add to them. Toppings and mix-ins like sugary syrups, heavy cream, or chocolate chips can significantly increase the calorie and sugar content of the meal. Healthy add-ons such as fresh fruit, nuts, and seeds or a drizzle of honey can enhance the nutritional profile without excessively boosting the calorie count.

Portion Control: Despite their health benefits, it’s crucial to watch portion sizes. Eating too much of any food, including overnight oats, can contribute to weight gain. Be mindful of the recommended serving sizes and listen to your body's hunger cues to avoid overeating.

As per the evidence, incorporating overnight oats into your diet can be part of a weight management strategy if prepared and consumed mindfully. By balancing the ingredients and servings, you can enjoy a nourishing breakfast that supports your health goals.

Digestive Health Benefits and Concerns

When it comes to understanding the effects of overnight oats on digestive health, it's crucial to examine both the benefits they can offer and the concerns they might raise. Digestive health is a complex area affected by various factors, including the type of foods we eat, the combination of nutrients present in them, and individual health conditions. Let's delve deeper into how overnight oats can interact with your digestive system.

Digestive Health Benefits of Overnight Oats:

  • Rich in Soluble Fiber: Overnight oats are a whole grain and a great source of soluble fiber, mainly beta-glucan. A meta-analysis published in the European Journal of Clinical Nutrition highlights that beta-glucan can be beneficial for digestion by increasing bowel movement regularity and softening stool, thus reducing constipation risk.
  • Prebiotic Effect: The soluble fiber in oats also serves as a prebiotic, which feeds the beneficial bacteria in the gut microbiome, as noted by research in the British Journal of Nutrition. A healthy microbiome is associated with improved gut health and a lower risk of intestinal issues.
  • Improved Nutrient Absorption: By soaking oats overnight, the starches break down and reduce phytic acid levels, which can improve nutrient absorption. This soaking process can make it easier for your body to access and utilize the minerals in oats, such as iron and zinc.

Potential Digestive Concerns with Overnight Oats:

  • Gluten Contamination: For individuals with celiac disease or gluten sensitivity, it's critical to choose oats that are certified gluten-free. While oats are naturally gluten-free, they can be contaminated with gluten during processing. Ingesting gluten-contaminated oats can lead to serious digestive issues for sensitive individuals.
  • High Fiber Content: Although fiber is beneficial, a sudden increase in fiber intake, which may occur when adding overnight oats to the diet, can cause gastrointestinal distress for some individuals. Symptoms may include bloating, gas, or discomfort, particularly in those who aren't used to a high-fiber diet.
  • FODMAPs Sensitivity: Oats contain fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs), which can trigger symptoms in those with irritable bowel syndrome (IBS) as per research in the Journal of Gastroenterology and Hepatology. FODMAP-sensitive individuals may need to moderate their intake of oats and monitor their reaction.

While overnight oats offer numerous digestive benefits, they should be incorporated into your diet with consideration for your individual digestive health needs. If you have specific digestive health concerns or a history of gastrointestinal issues, consulting with a healthcare professional or registered dietitian before making significant changes to your diet, including the introduction of overnight oats, is advisable.

Potential Allergens and Food Sensitivities Associated with Oats

Oats are a popular breakfast option, often praised for their nutritional benefits—packed with fiber, protein, and important vitamins and minerals. However, it's important to address that oats can sometimes be a source of allergens or cause food sensitivities for some individuals. Awareness and understanding of these concerns help individuals make better dietary choices that align with their personal health needs.

Celiac Disease and Gluten Sensitivity

Oats themselves do not contain gluten, a protein that causes health problems for those with celiac disease or gluten-sensitive individuals. However, due to common processing practices, oats are often contaminated with gluten from wheat, barley, or rye. This cross-contamination can make a seemingly safe food problematic for those with gluten-related disorders. It is recommended to opt for certified gluten-free oats if you fall under this category.

  • Look for labels stating 'certified gluten-free' to avoid cross-contamination.
  • Even gluten-free oats may cause symptoms in a small percentage of people with celiac disease, so monitor your individual response.

Oat Allergy

Though less common, some people may have an oat allergy, where the immune system mistakenly identifies proteins found in oats as a threat, triggering an allergic reaction. Symptoms of an oat allergy can include skin rashes, nasal congestion, difficulty breathing, and digestive issues.

  • If you suspect an oat allergy, consult with an allergist for proper testing and diagnosis.
  • Always read ingredient labels carefully, as oats can be found in many products.

Avenin Sensitivity

Avenin, a protein found in oats, can also trigger adverse reactions in some individuals. Similar to gluten, avenin can cause inflammation and symptoms in people with avenin sensitivity. This sensitivity is rare but crucial to recognize for those who experience symptoms upon consuming oats.

  • Avoid oats if you experience symptoms such as bloating, abdominal pain, or diarrhea after consumption.

FODMAPs and Digestive Issues

Oats contain fermentable carbohydrates known as FODMAPs (Fermentable Oligo-, Di-, Mono-saccharides And Polyols), which can be difficult to digest for those with irritable bowel syndrome (IBS) or similar gastrointestinal sensitivities.

  • Those following a low-FODMAP diet may need to limit or avoid oats.
  • Serving size can impact tolerance—small amounts may be manageable for some individuals.

While oats can be a wholesome addition to many diets, it's essential to consider these potential allergens and food sensitivities. Everyone's body reacts differently, and what's beneficial for one person can be harmful to another. If you experience adverse reactions to oats, it’s worth discussing with a healthcare provider to determine the best dietary approach for your health and well-being.

Frequently asked questions

Overnight oats are not typically suitable for a strict low-carb or ketogenic diet as they are relatively high in carbohydrates. Individuals following these diets may need to seek alternative breakfast options that align with their macronutrient goals.

Yes, overnight oats can be included in a diabetic diet, thanks to their low glycemic index, which results in a slower rise in blood glucose. It's important to be cautious with sweeteners and fruit add-ins to ensure the meal remains low on the glycemic scale. Monitoring individual blood sugar responses will be essential to maintaining good glycemic control.

Yes, overnight oats can contribute to weight loss due to their high fiber content, specifically beta-glucan, which promotes satiety and may help control appetite. Their low glycemic index helps in managing blood sugar levels, minimizing insulin spikes that can lead to fat storage. However, portion control and mindful selection of toppings are essential to prevent calorie overload.

Soaking oats overnight helps break down starches and reduce phytic acid, which may improve nutrient absorption and digestion compared to cooked oats. The soluble fiber in overnight oats, particularly the beta-glucan, aids in promoting bowel regularity and gut health. However, for those not accustomed to high-fiber foods, a gradual introduction is recommended to avoid digestive discomfort.

Ask a question about Overnight Oats and our team will publish the answer as soon as possible.

Possible short-term side effects

  • bloating
  • gas
  • discomfort
  • digestive issues from gluten contamination

Possible long-term side effects

  • weight gain from excessive calorie addition
  • digestive distress
  • possible allergic reactions

Ingredients to be aware of

  • added sugars
  • gluten contamination
  • high caloric toppings
  • fodmaps
  • avenin


  • lowers cholesterol
  • stabilizes blood glucose
  • supports muscle repair
  • contributes to heart health
  • source of essential vitamins and minerals

Healthier alternatives

  • berries
  • unsweetened plant-based milks
  • natural sweeteners like stevia
  • certified gluten-free oats
  • low-calorie toppings
  • portion control

Our Wellness Pick (what is this?)

Bob's Red Mill Rolled Oats

  • Organic and Gluten-Free
  • Whole Grain Oats
  • Non-GMO
  • High in Fiber
  • Convenient 4-Pack
Learn More!

Thank you for your feedback!

Written by Diane Saleem
Published on: 02-20-2024

Thank you for your feedback!

Written by Diane Saleem
Published on: 02-20-2024

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