Side effects: Large doses can cause diarrhea, nausea, abdominal cramping and, in the event of extremely high intakes, a risk of death from cardiac arrest. Adults should not consume more than 350 mg per day of magnesium in a supplement, according to the NIH.
4. Probiotics/synbiotics
Probiotics are beneficial bacteria that live in your gut and help break down and digest food. You can get them from supplements or from fermented foods like kefir, sauerkraut and apple cider vinegar.
Early evidence indicates probiotics could be helpful when it comes to weight loss, says Dariush Mozaffarian, a cardiologist, public health scientist and director of the Food is Medicine Institute at Tufts University.
One 2018 review of 15 well-designed trials found that probiotics, either in foods or in supplements, helped overweight and obese people reduce their body weight and body fat. Other trials have linked probiotics to improvements in blood sugar levels.
Some manufacturers are combining probiotics with prebiotics, a type of fiber that feeds gut bacteria. Mozaffarian says he believes those combinations, called synbiotics, are promising.
“It won’t be magical – the pounds won’t melt away – but if you have a healthy microbiome, you may be more likely to be able to lose weight or at least not gain further weight,” he says.
Although few studies have examined the safety of probiotics, they have a long history of safety, particularly in healthy people, according to the NIH. If you have a weakened immune system, there is a greater risk of negative side effects from probiotics, so you should talk to your health care provider before taking them.
Side effects: If you have a weakened immune system, rare side effects may occur from taking probiotics. Talk to your health care provider before taking them.
5. Caffeine
Caffeine is a stimulant found in tea, guarana, yerba mate and other herbs that is often added to weight loss supplements. It can give you a jolt of energy, boost your metabolism and increase fat breakdown, Willis says.
“It is an excellent lipolytic agent,” Willis says. “By that I mean it helps liberate fatty acids from our fatty tissues, especially for cardiovascular exercise. It helps to increase fat burning.”
Studies have shown only a moderate weight loss effect, however. The National Institutes of Health says it “may help you lose a little weight or gain less weight over time.”
Willis says caffeine and other fat-burning supplements need to be accompanied by changes to diet and lifestyle. “If your diet and lifestyle isn’t going to be conducive to losing fat, fix that first,” he says. “It won’t help you if you’ve just eaten three double cheeseburgers with an order of fries and a milkshake.”
Many people experience side effects from caffeine such as a rise in blood pressure and heart rate, sleep problems, anxiety or jitteriness or gastrointestinal problems. In high doses, caffeine can cause vomiting, heart palpitations and seizures. The National Institutes of Health recommends no more than 500 mg a day.
Side effects: People with high blood pressure or heart problems should check with their health care provider before taking a supplement with caffeine. Side effects may include headache, insomnia, nervousness, irritability, frequent urination, fast heartbeat and muscle tremors, according to the Mayo Clinic.
6. Green tea extract
Green tea contains a class of phytochemicals that are known as antioxidants, Wiley says. Some people believe green tea extracts, sometimes called EGCG, contribute to weight loss by boosting energy expenditure and blocking fat absorption.
A few studies do seem to indicate that green tea extracts could make you burn more calories, even when you’re at rest. But there is conflicting research on whether supplements with green tea extracts can help you actually shed pounds, Wiley says. If anything, they have only a moderate effect.
Green tea may have other benefits, potentially protecting against heart disease and cancer. Experts warn that large doses could cause liver damage.
Side effects: Experts warn that large doses could cause liver damage. Signs may include yellowing of the skin or eyes, nausea and stomach pain. Other side effects may include anxiety, tremors, irritability and sleeping problems, according to the University of Rochester Medical Center.
7. Berberine
Berberine is a substance found in plants that has a long history of use in Ayurvedic and traditional Chinese medicine.
The most studied benefit of berberine is its ability to improve insulin resistance in people with diabetes, according to The Cleveland Clinic.
Early research also indicates berberine could help with weight loss. A 2022 review of 41 research trials published in Frontiers of Nutrition found that people who took berberine for at least eight weeks experienced significant drops in their weight, and their cholesterol levels also improved.
However, more evidence is needed, because many studies in the review had a high risk of bias, according to the National Center for Complementary and Integrative Health.
Side effects: GI symptoms such as nausea, diarrhea, bloating, and constipation. Berberine may also interact with prescription medications. As with all supplements, you should talk to your healthcare provider before taking it.
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