Diet influences body weight directly. Foods you eat can either lead to weight gain or support weight loss and its management. The rate at which the body absorbs food and its nutrients matters a lot. You have probably come across claims that slow-digesting foods are a good option for persons who want to slim down. Is that true? Are slow-digesting foods good for weight loss? What are slow-digesting foods in the first place? You’ll get answers to these and other questions you probably have in this article. 

Glycemic Index 

Before we get into a discussion about slow-digesting food, it’s important to address the glycemic index. The glycemic index (GI) is a value used to measure how much different foods increase blood glucose levels in the body. 

The story of glycemic index started in the mid-1970s when several groups realized the same amounts of carbohydrates in different foods induce different blood sugar reactions after consumption (1). Dr. David D. Jenkins was the first to develop the concept of glycemic index in 1980/81. Together with his colleagues at the University of Toronto, Dr. Jenkins was working toward finding the optimal and most beneficial diet for persons with diabetes (2). 

Different foods have different GI values. The classification of foods and GI ratings are as follows:

  • Low GI: 55 or less
  • Medium GI: 56-69
  • High GI: 70 or higher

Generally speaking, the lower the glycemic index value of food, the less it may influence blood glucose levels (3).

Factors that play a role in the glycemic index of foods include (4):

  • Physical form of the food
  • Processing
  • Associated fat in the food, which lowers GI
  • Types of sugar and starches in the food
  • Fiber content 
  • How fast the food is digested and absorbed 

Low- vs. High-Glycemic Foods 

As seen above, when we are talking about slow-digesting foods we refer to their glycemic index. You may wonder about the difference between foods with low and high GI. What does it mean when a food has a high or low GI, in the first place?

High-glycemic foods quickly elevate blood glucose and may cause various health problems if a person eats too much. They do so because the body can digest and absorb these foods in the bloodstream quickly. On the flip side, low-glycemic foods are slower to digest and absorb in the bloodstream. As a result, they raise blood sugar at a slower rate. A person experiences gradual rises in blood glucose and insulin as opposed to rapid increases after ingesting high GI foods.

Slow-Digesting Foods and Weight Loss

Slow-digesting foods, i.e. those with a low GI, are often dubbed suitable for weight loss and diabetes management. But, is there any truth in those claims? We’re going to discuss that subject in this section.

The Journal of Nutrition published a review of evidence on the metabolic effects of slow-digesting (low GI) foods. The researchers explained glycemic index could be an important determinant of metabolic risk. This is particularly evident in the fact the major carbohydrates sources in the Western diet usually have high GI values. Results of the review showed rapid weight loss could be a potential mechanism of action through which low GI foods reduce metabolic syndrome risk.

The driving force behind weight loss with low GI foods, according to the review, is an overall decrease in calorie consumption. Reduced intake of calories often stems from a significant limitation of food choices. As a person lowers intake of foods with a high glycemic index and focuses on low GI foods, the number of calories they consume lowers significantly. Additionally, low GI foods may increase levels of chemicals that suppress appetite. Satiating effects of low-glycemic foods also stem from their high protein content.

The initial weight loss from slow-digesting foods may be explained through a decrease in glycogen stores from the liver and muscle. Glycogen is a readily mobilized storage form of glucose. Each gram of glycogen is stored with about 3g of water. This means a person could theoretically drop 1-2kg (2.2-4.4lbs) within the first week of a low-glycemic diet due to significant glycogen decreases in liver and muscle and through excretion of liberated water in urine. This particular process may last about seven to 14 days depending on the rate of glycogen depletion. After that, weight loss slows down. 

Even though the text above shows slow-digesting foods i.e. low GI diet can help you drop a few pounds, you need to keep one thing in mind – loss of water and glycogen isn’t a proper measure of weight loss. For that reason, the stores of water and glycogen tend to be replenished as soon as a person stops with this diet (5).

A study from the American Journal of Clinical Nutrition compared the effectiveness of two moderate-carbohydrate diets and a low-fat diet with different glycemic index values on weight loss, satiety, inflammation, and metabolic risks. Scientists divided 122 obese and overweight adults into three different groups:

  • Moderate-carbohydrate diet and high GI
  • Moderate-carbohydrate diet and low GI
  • Low-fat and high GI 

Participants had to follow these dietary patterns for six months. Results showed significant differences in BMI at weeks 16 and 20 between these three groups. The greatest reduction in BMI was observed in the second group (moderate-carbohydrate diet and low GI). On the flip side, changes in BMI didn’t differ much between the other two groups, both of which included high GI foods. Additionally, the low GI group also experienced the most significant decreases in fasting insulin, insulin resistance.

Scientists concluded a low GI and energy-restricted diet containing moderate carbohydrate content could be more successful at reducing body weight and controlling the metabolism of glucose and insulin than other types of diets in the study (6).

The same journal, the American Journal of Clinical Nutrition, also published a study that investigated the long-term effects of low GI foods compared to a high GI diet. In this study, the scientists randomly assigned 203 healthy women to a low GI or high GI diet with small calorie restrictions. The primary outcome measure was the change in weight after 18 months. Scientists also analyzed secondary outcome measures such as insulin and lipids levels and hunger. It is worth noting only 60% of participants completed the study.

Low-glycemic foods led to a slightly better weight loss in the first two months of follow-up. However, about 12 months later participants from both low and high GI groups started to regain the weight. A study period (18 months) changes in weight weren’t that different between the groups. This led scientists to conclude long-term weight loss isn’t much different between low and high GI diets (7). In other words, the effects of consumption of low-glycemic foods on weight loss were positive in the short-term only. 

The February 2019 issue of the Obesity Reviews also published a paper that focused on the impact of low GI foods on weight loss. Researchers assessed 101 studies involving 109 study arms and 8527 participants. They found low GI diets led to small, yet significant improvements in BMI, body weight, LDL (bad) cholesterol, and total cholesterol overall. Persons with normal blood sugar levels who reached a difference in the glycemic index of at least 20 points experienced a greater weight loss and improved cholesterol management compared to their counterparts who achieved a relatively small GI reduction. 

Scientists concluded low GI foods, especially those that allow persons to achieve a significant decrease in GI, were effective for weight loss. At the same time, scientists emphasized the importance of efforts to increase compliance with the consumption of low-glycemic foods (8).

What we can conclude from the studies above is that consumption of slow-digesting foods has the potential to support weight loss. Since foods with low glycemic value are absorbed and digested slowly, a person stays full for longer. Suppressed appetite lowers calorie intake and promotes weight loss. However, it is also useful to mention most studies evaluated short-term effects only. Long-term effects didn’t yield significant changes in this department. A lot more research on this subject is necessary to understand the true potential of slow-digesting foods on weight loss. 

A Low-Glycemic Diet Could Burn More Calories

One of the most frustrating effects of weight loss maintenance is that it takes a lower and lower number of calories to remain the same. As you lose weight the body works more efficiently and requires fewer calories. As a result, it can be more difficult for a person to keep losing weight or maintain weight loss once they achieve it. Even though weight loss and its maintenance are challenging, it’s not impossible to achieve them. 

One study offered tools the scientists deem promising. A study, published in the Journal of the American Medical Association, compared the low-fat, low-carb, and low-glycemic diets to determine which one resulted in the greatest calorie-burning a day. The winner in this category was a low-carb diet while the worst effects were observed with a low-fat diet. On the other hand, a low-glycemic diet was in the middle but scientists describe it as more promising.

Why? 

The reason is simple, the low GI diet burned more calories during the day than other diets in the study. Additionally, subjects found it easier to adhere to a low GI diet than its counterparts over a long-term period.

Since slow-digesting foods are usually natural foods such as fruits, vegetables, whole grains, and legumes, they move slowly through the digestive system. In the process, they use more energy and burn more calories (9). Additionally, these foods may accelerate metabolism and reduce the feeling of hunger thus giving a person a biological advantage to maintain weight loss. 

Even though this eating pattern may be easier to stick to compared to low-fat and low-carb diets, it’s not easy to adhere to it. In fact, compliance is a big problem for persons who want to try the low-glycemic diet. The tricky compliance stems from the fact multiple factors influence how the body digests food. Excessive consumption of low GI foods can also be problematic if a person chooses options high in saturated fats and sugar (10).

Slow-Digesting Foods to Try

While further studies on this subject are necessary, introducing slow-digesting foods into your diet could be useful. Or you can increase their consumption in case they’re already on your menu to some extent. Instead of high GI foods, junk food, sweets, and calorie-laden foods, you may want to enrich your diet with the following options.

Vegetables

Vegetables are the cornerstone of a well-balanced diet. Whether you’re trying to slim down or maintain weight loss, you need to up the intake of vegetables. Below you can take a look at the GI score per 80g of different vegetables:

  • Carrots: 35
  • Sweet potato (150g): 44
  • Butternut squash: 51
  • Parsnip: 52
  • Yam (150g): 54
  • Sweet corn: 55

Keep in mind that starchy vegetables such as parsnips and pumpkins tend to have a higher GI, so plan your meals accordingly.

The Glycemic index of vegetables is greatly influenced by several factors including ripeness and storage, processing, and cooking. Basically, riper products have a higher glycemic index. Also, you need to keep in mind fresh vegetables release carbohydrates at a slower rate than mashed, juiced, and pureed vegetables.

Fruits

Fresh fruits usually have a low glycemic index. Bear in mind tropical fruits tend to have higher GI values. Some of the best examples of low GI fruits are presented below, see their score per 120g of fruit:

  • Plum: 24
  • Grapefruit: 25
  • Peach: 28
  • Apricot: 34
  • Strawberry: 40
  • Orange: 40
  • Apple: 40
  • Pear: 42
  • Grapes: 43

Quinoa

Quinoa is a great addition to a healthy diet. Their glycemic index is low; 150g of quinoa has a GI score of 53 (11). At the same time, quinoa is a great source of protein, vitamin B, and minerals such as iron and potassium. Being a versatile food, quinoa is easy to add to salads, porridge, soups, and other meals. Quinoa is suitable for persons with gluten sensitivities too.

Legumes

Most legumes have a low GI score of 50 or lower. Below is the GI score per 150g of different legume options:

  • Kidney beans: 19
  • Red lentils: 21
  • Pinto beans: 33
  • Butter beans: 36
  • Chickpeas: 36
  • Green lentils: 37

It’s also useful to mention legumes are an abundant source of fiber which suppresses appetite and may also contribute to successful weight loss (12). Legumes also supply the body with different vitamins and minerals including B-complex vitamins, copper, iron, phosphorus, magnesium, zinc, and manganese.

Other Foods to Try

Besides the above-mentioned slow-digesting foods, you may also want to enrich your diet with the following (13):

  • Dairy and dairy-free products
  • Nuts and nut butter
  • Mixed grain bread
  • Pumpernickel
  • Sourdough rye
  • Rye bread
  • Soy and linseed bread
  • Sourdough wheat bread

You can also eat in moderation foods that have no glycemic index due to the absence of carbohydrates. These foods include meat, fish, eggs, olive oil, seafood, just to name a few (14, 15).

Conclusion

Slow-digesting foods are foods with a low glycemic index. Since the body gradually digests and absorbs them, these foods promote appetite suppression and a feeling of fullness. Studies show they are good for weight loss, but research focusing on long-term results is necessary.

References: 

  1. https://pubmed.ncbi.nlm.nih.gov/1330533/
  2. https://www.news-medical.net/health/What-is-Glycemic-Index.aspx
  3. https://pubmed.ncbi.nlm.nih.gov/17992183/
  4. https://healthengine.com.au/info/glycaemic-index-gi#C4
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2654909/
  6. https://pubmed.ncbi.nlm.nih.gov/24787494/
  7. https://pubmed.ncbi.nlm.nih.gov/17823436/  
  8. https://pubmed.ncbi.nlm.nih.gov/30460737/
  9. https://jamanetwork.com/journals/jama/fullarticle/1199154
  10. https://www.npr.org/sections/thesalt/2012/09/10/160757730/low-and-slow-may-be-the-way-to-go-when-it-comes-to-dieting
  11. https://www.glycemicindex.com/foodSearch.php?num=927&ak=detail
  12. https://pubmed.ncbi.nlm.nih.gov/31174214/
  13. https://www.medicalnewstoday.com/articles/325586
  14. https://healthyeating.sfgate.com/foods-metabolize-slowly-1911.html
  15. https://www.medicalnewstoday.com/articles/324871

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