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                                                                   Exhibit 10.43

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                       TWIN LABORATORIES INC., as Issuer,

                                       and

                           THE GUARANTORS NAMED HEREIN

                                       and

                 STATE STREET BANK AND TRUST COMPANY, as Trustee

                          FOURTH SUPPLEMENTAL INDENTURE

                          Dated as of January 25, 2O00

                                       to

                                    INDENTURE

                  Dated As of May 7, 1996 as supplemented as of
                      December 1, 1997, as of May 14, 1998
                          and as of September 15, 1998

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                   10-1/4% Senior Subordinated Notes due 2006

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            FOURTH SUPPLEMENTAL INDENTURE, dated as of January 25, 2000, by and
among TWIN LABORATORIES INC., a Utah corporation (the "Company"), ADVANCED
RESEARCH PRESS, INC., a New York corporation ("Advanced"), TWINLAB CORPORATION,
a Delaware corporation formerly named TLG Laboratories Holding Corp. ("Holding
Company"), CHANGES INTERNATIONAL OF FORT WALTON BEACH, INC., a Florida
corporation ("Changes"), BRONSON LABORATORIES INC., a Delaware Corporation
("Bronson"), HEALTH FACTORS INTERNATIONAL, INC., a Delaware corporation ("Health
Factors"), PR NUTRITION, INC., a California corporation ("PR Nutrition"), and
Twinlab FSC Inc., a Barbados corporation ("FSC"), as Guarantors, and State
Street Bank and Trust Company, a Massachusetts bank and trust company (successor
to Fleet National Bank), as Trustee (the "Trustee").

            WHEREAS, the Company, Advanced, Holding Company and Fleet National
Bank, as Trustee, executed an Indenture, dated as of May 7, 1996 (the
"Indenture"), in respect of $100,000,000 aggregate principal amount of the
Company's 10-1/4% Senior Subordinated Notes due 2006 (the "Securities");

            WHEREAS, State Street Bank and Trust Company is the successor to
Fleet National Bank, as Trustee under the Indenture;

            WHEREAS, the Company, Advanced, Holding Company, Changes and the
Trustee executed the First Supplemental Indenture dated as of December 1, 1997
(the "First Supplemental Indenture");

            WHEREAS, the Company, Advanced, Holding Company, Changes, Bronson,
Health Factors and the Trustee executed the Second Supplemental Indenture dated
as of May 14, 1998 (the "Second Supplemental Indenture");

            WHEREAS, the Company, Advanced, Holding Company, Changes, Bronson,
Health Factors, PR Nutrition and the Trustee executed the Third Supplemental
Indenture dated as of September 15, 1998 (the "Third Supplemental Indenture");

            WHEREAS, the term Indenture as hereinafter used in this Fourth
Supplemental Indenture shall mean the Indenture as amended by the First
Supplemental Indenture, the Second Supplemental Indenture and the Third
Supplemental Indenture;

            WHEREAS, Section 11.3 of the Indenture requires, under circumstances
specified in Section 11.3, that certain Subsidiaries of the Company execute and
deliver to the Trustee a supplemental indenture pursuant to which such
Subsidiaries of the Company shall be named as additional Subsidiary Guarantors;
and

            WHEREAS, all conditions and requirements necessary to make this
Fourth Supplemental Indenture a valid, binding and legal instrument in
accordance with its terms have

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been performed and fulfilled and the execution and delivery hereof have been in
all respects duly authorized.

            NOW, THEREFORE, in consideration of the above premises, each party
agrees, for the benefit of each other party and for the equal and ratable
benefit of the Holders of the Securities, as follows:

                                    ARTICLE I

                                   AMENDMENTS

            Section 1. The Company, Advanced, Holding Company, Changes, Bronson,
Health Factors, PR Nutrition and FSC and the Trustee hereby amend the Indenture
and agree that FSC shall be a Subsidiary Guarantor, a Guarantor and a Future
Subsidiary Guarantor for all purposes under the Indenture and each of the terms
"Subsidiary Guarantor", "Guarantor" and "Future Subsidiary Guarantor" shall for
all purposes under the Indenture specifically include FSC.

                                   ARTICLE II

                            MISCELLANEOUS PROVISIONS

            Section 2.1. Terms Defined. For all purposes of this Fourth
Supplemental Indenture, except as otherwise defined or unless the context
otherwise requires, terms used in capitalized form in this Fourth Supplemental
Indenture and defined in the Indenture have the meanings specified in the
Indenture.

            Section 2.2. Indenture. Except as amended hereby, the Indenture and
the Securities are in all respects ratified and confirmed and all their terms
shall remain in full force and effect.

            Section 2.3. Governing Law. THIS FOURTH SUPPLEMENTAL INDENTURE SHALL
BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW
YORK, AS APPLIED TO CONTRACTS MADE AND PERFORMED WITHIN THE STATE OF NEW YORK,
WITHOUT REGARD TO PRINCIPLES OF CONFLICT OF LAWS.

            Section 2.4. Successors and Assigns. All agreements of the Company,
Advanced, Holding Company, Changes, Bronson, Health Factors, PR Nutrition and
FSC in this Fourth Supplemental Indenture and the Securities shall bind their
respective successors and assigns.


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            Section 2.5. Multiple Counterparts. This Fourth Supplemental
Indenture may be executed in any number of counterparts, each of which shall be
an original; but such counterparts shall together constitute but one and the
same instrument.

            Section 2.6. Effectiveness. The provisions of this Fourth
Supplemental Indenture shall become effective immediately upon its execution and
delivery by the Trustee in accordance with the provisions of Article IX of the
Indenture.

            Section 2.7. Trustee Disclaimer. The Trustee accepts the amendment
of the Indenture effected by this Fourth Supplemental Indenture and agrees to
execute the trust created by the Indenture as hereby amended, but only upon the
terms and conditions set forth in the Indenture, including the terms and
provisions defining and limiting the liabilities and responsibilities of the
Trustee, which terms and provisions shall in like manner define and limit its
liabilities and responsibilities in the performance of the trust created by the
Indenture as hereby amended, and, without limiting the generality of the
foregoing, the Trustee shall not be responsible in any mariner whatsoever for or
with respect to any of the recitals (other than the second recital) or
statements contained herein, all of which recitals or statements are made solely
by the Company, Advanced, Holding Company, Changes, Bronson, Health Factors, PR
Nutrition and FSC or for or with respect to (i) the validity, efficacy or
sufficiency of this Fourth Supplemental Indenture or any of the terms or
provisions hereof, (ii) the proper authorization hereof by the Company,
Advanced, Holding Company, Changes, Bronson, Health Factors, PR Nutrition and
FSC by corporate action or otherwise, (iii) the due execution hereof by the
Company, Advanced, Holding Company, Changes, Bronson, Health Factors, PR
Nutrition and FSC, or (iv) the consequences (direct or indirect and whether
deliberate or inadvertent) of any amendment herein provided for, and the Trustee
makes no representation with respect to any such matters.

            Section 2.8 Headings. The headings of the Articles and Sections of
this Fourth Supplemental Indenture have been inserted for convenience of
reference only, are not to be considered a part hereof and shall in no way
modify or restrict any of the terms or provisions hereof.

                     [Remainder of Page Intentionally Blank]


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                                   SIGNATURES

            IN WITNESS WHEREOF, the parties hereto have caused this Fourth
Supplemental Indenture to be duly executed, all as of the date first written
above.


TWIN LABORATORIES INC.,                    TWINLAB CORPORATION,
as Issuer

By: /s/ Ross Blechman                      By: /s/ Ross Blechman
   --------------------------------           ----------------------------------
   Name: Ross Blechman                        Name: Ross Blechman
    Title: Chairman, CEO, President           Title: Chairman, CEO, President


ADVANCED RESEARCH PRESS,                   CHANGES INTERNATIONAL OF
INC.                                       FORT WALTON BEACH, INC.

By: /s/ Ross Blechman                      By: /s/ Ross Blechman
   --------------------------------           ----------------------------------
   Name: Ross Blechman                        Name: Ross Blechman
   Title: Executive Vice President            Title: Chairman


BRONSON LABORATORIES, INC.                 HEALTH FACTORS
INTERNATIONAL, INC.

By: /s/ Ross Blechman                      By: /s/ Ross Blechman
   --------------------------------           ----------------------------------
   Name: Ross Blechman                        Name: Ross Blechman
   Title: Chairman, CEO, President            Title: Chairman, CEO, President


TWINLAB FSC INC.                           PR NUTRITION, INC.

By: /s/ Ross Blechman                      By: /s/ Ross Blechman
   --------------------------------           ----------------------------------
   Name: Ross Blechman                        Name: Ross Blechman
   Title:                                     Title: Chairman & CEO


STATE STREET BANK AND TRUST
COMPANY, as Trustee

By: /s/ Elizabeth C. Hammer
   --------------------------------
   Name:   Elizabeth C. Hammer
   Title:    VICE PRESIDENT


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