Lutein, a well-known carotenoid primarily recognized for its role in eye health, is garnering increasing attention for its potential benefits in weight management and overall metabolic health. This article explores the emerging research on lutein, its mechanisms of action, and its potential role in a comprehensive weight loss strategy.
What is Lutein?
Lutein is a type of carotenoid, a class of naturally occurring pigments responsible for the vibrant yellow, orange, and red colors in many fruits and vegetables. Specifically, lutein is a xanthophyll, a type of carotenoid that contains oxygen. Carotenoids, including lutein, are essential nutrients that humans cannot synthesize, requiring dietary intake through food or supplements. Lutein is often found alongside another carotenoid called zeaxanthin, and both are known for their antioxidant properties.
Lutein's Established Role in Eye Health
The link between lutein and eye health was first reported in 1994. Lutein and zeaxanthin are concentrated in the macula, a region of the retina responsible for central vision. Here, they act as antioxidants, protecting the eye from light-induced oxidative damage, particularly from blue light. Numerous studies support the importance of lutein in preventing age-related macular degeneration (AMD). A study showed that lutein and zeaxanthin play a significant role in preventing age-related macular degeneration (AMD) by blocking harmful blue light and may also help with diabetic retinopathy, retinal detachment, and uveitis. The Age-Related Eye Disease Study (AREDS) demonstrated that a supplement containing lutein and zeaxanthin reduced the risk of advanced AMD by 25% over 5 years in individuals already diagnosed with the condition.
Emerging Evidence: Lutein and Weight Loss
Recent research suggests that lutein may offer benefits beyond eye health, particularly in the realm of weight management. Studies indicate that lutein might influence body composition and cholesterol levels, especially when combined with a low-calorie diet in middle-aged obese individuals.
Study Highlights: Lutein Supplementation and Low-Calorie Diet
One notable study published in the British Journal of Nutrition investigated the effects of lutein supplementation in conjunction with a low-calorie diet on obese middle-aged individuals.
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Study Design: The randomized, double-blind, placebo-controlled trial involved 48 obese middle-aged participants who were assigned to a low-calorie diet with either a placebo or a lutein supplement for 10 weeks.
Key Findings:
- Both groups experienced significant reductions in body weight and waist circumference.
- The lutein group exhibited a greater decrease in the percentage of body fat compared to the placebo group.
- The placebo group experienced a significant decline in fat-free mass, while the lutein group did not.
- Visceral fat and serum levels of total cholesterol (TC) and LDL-cholesterol were significantly decreased only in the lutein group.
Potential Mechanisms of Action
Researchers propose several mechanisms through which lutein may exert its beneficial effects on body composition and lipid profiles:
- Interaction with Nuclear Receptors: Lutein could improve body composition by interacting with nuclear receptors such as the retinoic acid receptor, retinoid X receptor, and PPAR, leading to an increase in energy expenditure.
- Improved Lipid Profiles: Lutein may improve lipid profiles by enhancing the activity of LDL-cholesterol receptors and scavenger receptor class B type 1, both of which are involved in the removal of LDL from plasma and cholesterol from peripheral tissues, ultimately reducing plasma cholesterol levels.
Additional Research Supporting Lutein's Role in Metabolic Health
Multiple studies suggest that lutein may play a role in preventing metabolic disease through its antioxidant and anti-inflammatory properties. Epidemiological studies have linked higher dietary intake and serum levels of lutein with decreased adiposity.
- One study, involving 120 people with central obesity, explored the effect of 10 mg daily lutein supplementation for 12 weeks on serum lutein, glycemic and lipid profiles, inflammatory factors, and body composition.
- Animal studies have shown that lutein treatment decreased body weight and abdominal and total adipose tissue in mice fed a high-fat diet, along with reduced levels of total cholesterol (TC), triglycerides (TGs), and low-density lipoprotein cholesterol (LDL-C).
Lutein and Appetite Control
Research presented at Obesity Week 2016 highlighted the potential of "early time restricted eating" to improve fat oxidation and reduce daily ups and downs in hunger levels.
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- Early Time Restricted Eating: This strategy involves eating dinner very early or even skipping it, confining food intake to a shorter daily timeframe to align with metabolic activities that function more optimally in the morning.
- Improved Metabolic Flexibility: Early time-restricted eating improved the ability to move between burning carbs and fat, a process that can be impaired in individuals with insulin resistance.
Lutein's Broader Health Benefits
Beyond weight management and eye health, lutein offers a range of additional health benefits:
- Cognitive Function: Lutein is found in brain tissues and is considered the predominant carotenoid in the brain. Studies suggest that lutein supplementation may improve cognitive function, including learning, thinking, reasoning, and remembering.
- Cardiovascular Health: Lutein and zeaxanthin can help HDL ('good' cholesterol) particles grow, which helps remove extra cholesterol from your bloodstream and sends it to your liver for removal through your stool. Research shows that increasing HDL can be heart protective.
- Skin Protection: Lutein and zeaxanthin can protect your skin by absorbing harmful blue light, which can help reduce or slow the signs of aging. A study shows that a zeaxanthin and lutein supplement may help improve skin hydration, elasticity, and inflammation.
- Anti-inflammatory Properties: Lutein's anti-inflammatory properties may contribute to its protective effects against various chronic diseases.
Dietary Sources of Lutein
Lutein cannot be synthesized by humans and must be obtained through diet or supplements. Good sources of lutein include:
- Dark, leafy green vegetables (kale, spinach, collard greens)
- Egg yolks
- Broccoli
- Peas
- Avocado
- Parsley
- Oranges
- Honeydew melon
- Kiwis
- Red peppers
- Squash
- Red grapes
- Corn
- Durum wheat
The average dietary intake of lutein is often below recommended levels. Studies have shown that the median intake of lutein is far below the proposed level, highlighting the importance of incorporating lutein-rich foods into the diet or considering supplementation.
Lutein Supplementation: Considerations and Recommendations
Lutein supplements are generally considered safe, but it’s important to note that taking a lutein supplement may lower your blood sugar and can cause yellowing of the skin. Lutein is best absorbed when taken with a high-fat meal - think avocados, cheese, salmon, and nuts.
Dosage
While a typical diet contains 1-3 mg of lutein per day, most benefits have been shown at 6 mg per day, which can be achieved through consuming food sources of lutein. Most supplements contain 20 mg or more, which is much higher than the amount needed to get the benefits of lutein. However, most studies on lutein have used doses from 10-40 mg per day and have not found any adverse effects. An observed safe level (OSL) of 20 mg/d for lutein has been suggested.
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Safety
Lutein is categorized as Generally Regarded as Safe (GRAS), meaning that research has not found a significant link between regular lutein consumption and adverse side effects. However, high intakes of xanthophylls, in general, have been linked to an increased risk of skin and stomach cancers. While results from these studies were not found to be significant, more research is needed to confirm safe and optimal doses of xanthophylls such as lutein.
Recommendations
- Consult a Healthcare Provider: Before adding lutein supplements to your diet, it’s a good idea to talk with your doctor.
- Third-Party Testing: Look for products that have been tested by a third party such as USP or NSF.
Lutein and Central Obesity
Central obesity, characterized by excessive abdominal fat, is associated with increased production of inflammatory factors and metabolic risk factors. Lutein might retard the development of metabolic disease through its antioxidant and anti-inflammatory properties. Epidemiological studies have associated higher dietary intake and serum levels of lutein with decreased adiposity.
Lutein and Exercise
In a study published in PLoS One (2), it was found that giving rats lutein would increase the distance they ran ‘voluntarily’ in the wheel during their spare time. In the study, rats were given either lutein, full fat milk or a combination of lutein and full fat milk over the course of several months. The rats were then observed in their cages to see if they would voluntarily use the treadmill and the distance covered was measured. After about 5-6 weeks, the milk and lutein group started running much more than the other rats - to the tune of about 30km.
CPT1
Researchers then examined the muscle cells of the mice and found increased amounts of CPT1 or ‘carnitine palmitoyltransferase’. The increase in CPT1 in turn was observed to be triggered by an increase in AMPK. AMPK is produced when the muscles are low on energy in order to ‘turbocharge’ the mitochondria.
AMPK
Increasing AMPK is something that is generally of interest and many studies are demonstrating the key role it plays in energy and weightloss. AMPK, or ‘AMP-activated protein kinase’, is a ‘heterotrimeric compound’ meaning it’s a molecule made from three separate parts. As mentioned, it acts as a signal to that cellular energy is dropped - i.e. when ATP (Adenosine Triphosphate) is low in the cells and/or when glycogen is low in the muscles. This then tells the cells to amp up energy production and to become more efficient as well as increasing fat oxidation.