Spirulina: A weight loss aid?

Obesity^[1] is a global health concern that can be largely mitigated by healthy lifestyle choices^[2]. For people who already have obesity, behavioral interventions based on changes to diet and exercise habits are a first-line treatment option. However, adherence can vary among people depending on a host of factors, with many people wishing they could just take a pill^[3] instead. Why not both?

Spirulina^[4] is a blue-green algae (cyanobacteria) that has emerged as a trendy ‘superfood’ supplement due to its high phytochemical (phenolic compounds, carotenoids, and tocopherols) and essential nutrient content (proteins, n-3 and n-6 fatty acids). Recent studies, mostly done in animals, have demonstrated the antioxidant^[5], anti-inflammatory^[6], and blood-lipid lowering^[7] activity of spirulina, attributable to its phytochemicals. Lower body fat, mass, and blood lipid concentrations were demonstrated^[8] in mice administered a high fat diet and spirulina when compared to mice only fed a high fat diet.

A couple of human trials have evaluated the influence of spirulina, finding slight improvements in body composition and blood lipids. One study^[9] had obese participants supplement with one gram of spirulina per day for 12 weeks and reported slightly reduced bodyweight, total cholesterol, and appetite more than placebo. Another study^[10] supplemented obese individuals with two grams of spirulina per day, also for 12 weeks, and also demonstrated slight reductions in bodyweight and triglycerides, when compared to placebo.

Spirulina studies suggest several benefits that could apply to overweight and obese people. However, few controlled studies have evaluated the effect of spirulina supplementation, let alone spirulina intake in combination with exercise, on markers of obesity and cardiovascular disease risk in humans. The authors of the study under review designed a double-blind, randomized, crossover controlled trial to assess changes in body composition and cardiorespiratory fitness.

Obesity and excess weight are major risk factors for cardiovascular disease and are preventable with behavioral intervention. Spirulina is a nutraceutical that has demonstrated antioxidant, anti-inflammatory, and hypolipidemic activity in animal studies. The authors of the study under review designed a double-blind, randomized, crossover controlled trial to evaluate the effect of spirulina supplementation with and without concomitant exercise on body composition and cardiorespiratory fitness since no controlled human studies currently exist.

This was a 12-week double-blind, randomized, crossover controlled trial of 52 sedentary overweight (n=27) or obese (n=25) male participants evaluating the effects of Spirulina maxima supplementation paired with and without exercise on body composition and cardiorespiratory fitness. Participants were excluded if they drank alcohol, took drugs or supplements, had a chronic disease, or could not practice physical exercise.

The study protocol is laid out graphically in Figure 1. In the study, participants were randomized into the exercise (n=28) or no exercise arm (n=24) and further separated into those supplementing with spirulina (4.5 grams per day) or a placebo, totaling to four groups: 1) spirulina and exercise, 2) exercise control, 3) spirulina alone, 4) control (placebo alone). The two six-week treatment periods were separated by a two-week washout period. Group allocations were performed by an independent researcher and, to help monitor compliance, participants had to pick up their capsules every week at the laboratory.

Each participant performed a maximum intensity stress test (on a cycle ergometer) and completed three 24-hr dietary recalls before and after each treatment period. A food frequency questionnaire was administered before and after intervention to verify total energy and macronutrient intake and both dietary measures were monitored by two trained nutritionists.

Participants in the exercise groups performed 20-30 minutes each of muscular endurance and cardiovascular exercise, totaling about one hour of exercise per day for five days per week. The cardiovascular exercise had to be performed at 50-80% of the participant’s heart rate reserve for three of the days and 80-90% of heart rate reserve for the other two days. The exercise protocol was performed under technical supervision of a trainer.

The primary outcomes of this preregistered^[11] study were changes in blood lipids (triglycerides, and total, HDL, and LDL cholesterol). Secondary outcomes were markers of cardiorespiratory fitness, oxidative stress, and body composition. However, the authors stated the primary outcome to be body composition in the manuscript being reviewed and did not report on blood lipids or markers of oxidative stress. No reason for this change was provided, and no correction for multiple comparisons was conducted.

This two-by-six-week (two-week washout) crossover, double-blind RCT of 52 sedentary overweight or obese male participants evaluated the effects of Spirulina maxima supplementation (4.5 grams per day) paired with and without exercise on body composition, cardiorespiratory fitness, and redox status.

The exercise-only group did not lose more weight compared to control, while both spirulina-only and the spirulina plus exercise group lost a similar amount of weight: around two kilograms.

As you can see in Figure 2, all intervention groups lost a similar amount of body fat compared to the control group—differences that were statistically significant but of little clinical value, as the drop was of about 1%. These changes were similar between overweight and obese participants, when analyzed separately, but the overweight participants experienced far more variability in their response to the interventions.

Only the time to fatigue improved when evaluating cardiorespiratory fitness in both spirulina-supplemented groups compared to both the exercise-only and control groups, which did not differ significantly for changes in these variables. Changes in the onset blood lactate accumulation and resting heart rate were all pretty minor. All groups similarly increased maximal oxygen consumption compared to the control group.

No differences in energy intake were noted between groups or within groups during the intervention. No adverse events of spirulina supplementation were observed.

Both groups supplemented with spirulina demonstrated single digit percentage improvements in body composition and cardiorespiratory fitness when compared to placebo. The benefits were more pronounced for obese vs. overweight individuals.

This is the first study to suggests that spirulina has effects on body composition and cardiorespiratory fitness and that supplementation can provide benefits alongside exercise. The authors did their best to control several variables, such as having a nutritionist and trainer monitor participants to help them maintain an isocaloric diet and their exercise protocol, respectively. With these controls in place, the overall improvements due to spirulina were found to be quite small.

Generally, it is recommended^[12] to lose about 0.5-1.0 kilograms of bodyweight (one to two pounds) per week by making persistent changes to diet and exercise habits (reduction of intake, increase of expenditure). The study at hand demonstrated a loss of roughly two kilograms over a six-week period from spirulina alone and in combination with exercise, respectively, meaning spirulina might help jumpstart adequate weight loss, but it’s unclear whether the improvements would continue with further supplementation or whether they would revert after stopping.

Nevertheless, the study seems to confirm that the provision of 4.5 grams per day of spirulina may support the beneficial effects of exercise (and potentially other lifestyle changes) on the body composition and fitness of overweight and, even moreso, obese individuals. What should be clear, however, is that spirulina supplements alone will not solve the initially characterized obesity crisis. Moreover, the extra kilogram lost in the spirulina plus exercise group above the only-spirulina group was not statistically significant. Future studies will have to evaluate the ability of spirulina to promote diet-induced weight loss in a study of participants with reduced energy intake and longer follow-up to evaluate if the effect remains without further spirulina supplementation.

One meta-analysis^[13] of 45 prospective cohort studies did suggest that risk of cardiovascular disease, stroke, sudden death, and non-cardiovascular disease increases with 10 bpm increments above 60-70 bpm. The changes in cardiorespiratory fitness may initially seem to be of similarly low practical relevance; and indeed, a reduction in resting heart rate by two or three beats per minute (bpm) is not likely to have a meaningful impact on health when the natural range of resting heart rate is between 60 and 100 beats per minute^[14]. Moreover, the significance may depend on various factors^[15] including population, disease-state, and even posture.

The increase in VO_2max, on the other hand, is notable in light^[16] of a study that associated a VO_2max increase of 1 mL/kg/min in men with a 9% relative risk reduction of all-cause mortality in a multivariate analysis—that's particularly relevant for obese individuals for whom a significant approximate 2% increase in VO_2max occurred even in the absence of exercise. It should be mentioned, though, that the previously cited study was of observational design and cannot prove causation. Moreover, the authors of the study under review note that the slight increases in VO_2max could be due to body mass loss rather than an improvement in cardiovascular fitness (because the measurement is scaled by bodyweight^[17] in kilograms).

While the crossover design, the specific participant group, and the rigorous control are strengths of the study, they also limit the study's generalizability. For example, conclusions cannot be drawn regarding how supplementation may affect healthy or athletic populations. Furthermore, the study fails to provide evidence as to which of the variety of compounds present in spirulina are responsible for these findings, let alone uncover any mechanistic understanding.

This is the first study to suggests that spirulina has effects on body composition and cardiorespiratory fitness and may supplement benefits from exercise, but the changes are modest. The absolute improvements in body composition, heart rate, and at least for the overweight participants, fitness, are small and unlikely to translate to meaningful reductions in cardio-metabolic disease. The study also fails to provide novel insights into the agents and mechanisms behind the observed benefits and its results cannot be generalized uncritically to other subgroups of the general population, including women, elderly people, lean or athletic individuals, and others.

In animal studies, spirulina has demonstrated^[8] to be able to suppress fat cell development as well as increase fat cell browning. Brown fat cells^[18] are associated with fat loss because they use the energy stored as heat when exposed to cold temperatures. Spirulina also exhibits protective effects^[19] against oxidative stress and dyslipidemia. A systematic review^[20] concluded spirulina could be used as a therapeutic supplement for metabolic syndrome (a group of conditions associated with cardiovascular disease and diabetes) and non-alcoholic fatty liver disease for its potential effects on hypertension^[21] and appetite suppression^[22], and powerful antioxidant capacity^[7]. However, whether these attributes of spirulina translate to modest weight loss or improved cardiorespiratory fitness, as was reported in the study under review, is unclear.

One RCT reported similar improvements in bodyweight to the study under review following spirulina supplementation. The three-month^[23] supplementation trial of 40 hypertensive participants demonstrated a significant reduction of bodyweight (five kilogram reduction) and BMI (two-point reduction) in the supplementation group (two grams per day), when compared to placebo. Another three-month trial^[24], this time evaluating the hypolipidemic effects of spirulina supplementation (one gram per day) in participants with dyslipidemia found improvements in the lipid profile but no changes in bodyweight and BMI.

In comparison to the study at hand, both trials used significantly lower amounts of spirulina and one reported greater weight reduction, while the other did not report any. These studies suggest that higher dosage of spirulina supplementation could maximize the slight improvements in body composition, but more research is necessary. While it was neither a primary nor secondary outcome of the study, it is worth pointing out that previous research^[25] found that, although cyanobacteria are known heavy metal accumulators, an analysis of 25 commercial spirulina products exhibited heavy metal levels significantly below present regulation levels and a preliminary animal study^[26] suggest it may also help limit the negative effects of heavy metals in the body.

The low levels of heavy metals are also relevant because supplementing with spirulina has been shown to have beneficial antioxidant effects^[27] that may reduce oxidative stress caused by intense exercise and further lead to cardiorespiratory fitness improvement. In a small study^[28] evaluating the effect of spirulina supplementation (six grams per day) over four weeks in nine recreational runners training at least two days a week for 45 minutes, time to fatigue was improved by about 40 seconds. Two studies evaluating the effect of spirulina supplementation on lactate concentration over 15 days in recreational runners^[29] before and after exercise days (n=41, five grams per day) and over three weeks in young students^[30] before maximal athletic activity (n=16, 7.5 grams per day) found slight and significant decreases in lactate concentrations, respectively. The results of these studies align with the findings of improved cardiorespiratory fitness from the study under review, but they still leave questions about supplementation dosage and duration for optimal benefit as well as clinical effectiveness toward CVD risk reduction.

While preliminary studies of spirulina have reported suppression of fat cell development, hypertension and appetite, as well as a high antioxidant capacity, other intervention trials have demonstrated bodyweight and cardiorespiratory benefits similar to those from the study under review and reveal the infancy of this area of research. Future studies addressing optimal dosage and duration of spirulina supplementation, along with the clinical significance of the resultant changes are necessary.

Q. What else is spirulina good for?

A review^[31] of primarily clinical studies concluded that adequate evidence supports the use of spirulina for allergies (drippy nose, itchy throat, etc.) as its main potential use, while chronic fatigue and anti-viral applications were ruled out for lack of high-level evidence trials.

There have been suggestions for the use of spirulina to help treat cancer^[32], blood glucose^[33], blood pressure, and blood lipid profile as well as hypercholesterolemia^[34] and atherosclerosis^[35] in cell and animal studies. The results of a recent meta-analysis relevant to some of these is shown in Figure 3.

Spirulina is also a good source^[36] of vitamins B1, B2, B12, and E, as well as iron, calcium, magnesium, phosphorus, and potassium and may thus be used to improve the micronutrient content of otherwise nutrient-deficient diets. However, the vitamin B12 in spirulina is predominantly pseudovitamin B12^[37], which is inactive and cannot be absorbed by humans. In addition, the selenium from spirulina^[38] may not be nearly as bioavailable as other sources.

Q. Are there different kinds of spirulina?

There are 15 different species of the blue-green algae^[39] (cyanobacteria). Spirulina belongs to the Spirulina as well as Arthrospira genera. The reason for the spillover into other genera is that Arthrospira was discovered later and exhibits a separation into two chambers (septum), but shares the helical morphology of Spirulina. Since then, although they are slightly different, the name “spirulina” stuck and became common for scientists and then consumers.

Only three of the species—Spirulina platensis, Spirulina fusiformis, and Spirulina maxima—have been extensively investigated^[7] and demonstrate similar nutritional composition and potential effects. Moreover, since these algae are cultivated around the world, the differences between species as well as cultivation practices (i.e. different minerals in the water they are growing in) will change their nutritional and potential medicinal properties.

Spirulina is a blue-green algae that has antioxidant and hypolipidemic properties and could potentially support behavioral lifestyle interventions in obese and overweight individuals. This two-by-six-week crossover (two-week washout), double-blind, RCT of 52 sedentary overweight or obese male participants evaluated the effects of Spirulina maxima supplementation paired with and without exercise on body composition and cardiorespiratory fitness.

While the spirulina supplementation yielded small individual and additive effects on top of exercise, especially in obese participants, the clinical impact of these changes from a six-week supplementation duration and 4.5 grams per day dosage is not clear. Possible confounders of its efficacy are both the duration and dosage. Optimal values for both will have to be determined in future research.