Revenue increased 55.3% to $264.9 million in the fourth quarter of 2020, and we continue to execute strongly across all areas of the business.
Earnings per diluted share were $2.36, a 42.2% increase over the prior year period.
For the fourth quarter, income from operations was $38 million, an increase of 103% versus the same period last year.
Growth was driven by significant year-over-year and sequential improvements in the number of active earning OPTAVIA Coaches, which grew to 44,200 in the fourth quarter, another new record.
Additionally, productivity per active earning coach increased 13.4% to $5,932 during the quarter compared to the prior year period.
The company's focus continues to be supporting our growing community of independent OPTAVIA Coaches as they develop and focus on the four competencies that drive our business success, namely, attracting new clients, supporting clients on the Optimal Weight 5&1 Plan and supporting new coaches and developing coach leaders.
We remain on track to support a $2 billion revenue business by the end of 2021, creating ample headroom for several years depending on the trajectory of future growth.
We will also launch the beta version of the OPTAVIA client app, which focuses on meal planning on the OPTAVIA Weight 5&1 plan.
The U.S. weight loss market that is core to OPTAVIA's business has been growing at about 6% per annum and is worth $20 billion today.
Roughly 70% of the U.S. population is overweight or obese, and this segment is growing at 2% per annum, which highlights the importance of a proven health and wellness solution like the one we offer.
Around 63% of Americans report that they have adopted new positive health routines since March of 2020.
And of those, 96% plan to continue embracing healthy habits this year.
Revenue in the fourth quarter of 2020 increased 55.3% to $264.9 million from $170.6 million in the fourth quarter of 2019.
As Dan highlighted, we achieved another record quarter of active earning coaches ending the quarter with 44,200.
This represents 39% growth as compared to 31,800 coaches in the same period last year and a 5% increase from the end of the third quarter of 2020.
Average revenue per active earning coach for the quarter was 5,932 and compared to 5,229 for the fourth quarter of 2019 and down $6,329 in the third quarter of 2020, mainly due to timing of promotional activity from one quarter to another.
OPTAVIA branded products grew to 87.2% of our total company consumable units sold in the fourth quarter, up from 79% in the prior year period.
Gross profit for the fourth quarter of 2020 increased 55.6% to $199.2 million compared to $128.1 million in the prior year period.
Gross profit as a percentage of revenue was 75.2%, a slight increase compared to 75.1% in the fourth quarter of 2019.
SG&A for the fourth quarter of 2020 increased $51.9 million to $161.3 million compared to $109.4 million for the fourth quarter of 2019.
SG&A as a percentage of revenue decreased 320 basis points year-over-year to 60.9% versus 64.1% in the fourth quarter of 2019.
Income from operations increased $19.3 to $38 million from $18.7 million in the prior year period, primarily as a result of increased gross profit, partially offset increased SG&A expenses.
Income from operations as a percentage of revenue was 14.3% for the quarter, an increase of 340 basis points from the year-ago period.
The effective tax rate was 26% for the fourth quarter of 2020 compared to 22.4% for the September 30, 2020 year-to-date and compared to a tax benefit of 4.7% in the year-ago period.
During the fourth quarter of 2020, the effective tax rate increased 3.8%, which reduced earnings per diluted share by $0.12 due to a discrete tax reserve recorded during the period.
For the full year of 2020, earnings per diluted share was negatively impacted by $0.12 due to this discrete tax reserve.
The fourth quarter of 2019 tax benefit reflected the impact of federal tax benefits from share-based compensation, partially offset by increases in the effective state tax rate of 2%.
Net income in the fourth quarter of 2020 was $28 million or $2.36 per diluted share, based on approximately 11.9 million shares outstanding.
This compares to net income of $19.9 million or $1.66 per diluted share-based on approximately 11.9 million shares outstanding in the prior year.
Our balance sheet remains very strong with cash, cash equivalents and investment securities of $174.5 million as of December 31, 2020, compared to $92.7 million at December 31, 2019.
Our Board of Directors declared a quarterly cash dividend in the fourth quarter of $13.4 million or $1.13 per share, which was paid on February 5, 2021.
There was -- there are approximately 2,323,000 shares of common stock remaining under our stock repurchase program.

Summary:
Revenue increased 55.3% to $264.9 million in the fourth quarter of 2020, and we continue to execute strongly across all areas of the business.
Earnings per diluted share were $2.36, a 42.2% increase over the prior year period.
Revenue in the fourth quarter of 2020 increased 55.3% to $264.9 million from $170.6 million in the fourth quarter of 2019.
Net income in the fourth quarter of 2020 was $28 million or $2.36 per diluted share, based on approximately 11.9 million shares outstanding.